FORUM – ASSESSING THE PUBLIC HEALTH EFFECTS OF THE LEGALIZATION OF RECREATIONAL CANNABIS USE

Assessing the public health impacts of legalizing recreational cannabis use: the US experience

Wayne Hall1,2, Michael Lynskey2 1University of Queensland Centre for Youth Substance Abuse Research, Brisbane, Australia; 2National Addiction Centre, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK

The sale of cannabis for adult recreational use has been made legal in nine US states since 2012, and nationally in Uruguay in 2013 and Canada in 2018. We review US research on the effects of legalization on cannabis use among adults and adolescents and on cannabis-related harms; the impact of legalizing adult recreational use on cannabis price, availability, potency and use; and regulatory policies that may increase or limit adverse effects of legalization. The legalization of recreational cannabis use in the US has substantially reduced the price of cannabis, increased its potency, and made cannabis more available to adult users. It appears to have increased the frequency of cannabis use among adults, but not so far among youth. It has also increased emergency department attendances and hospitalizations for some cannabis-related harms. The relatively modest effects on cannabis use to date probably reflect restrictions on the number and locations of retail cannabis outlets and the constraints on commercialization under a continued federal prohibition of cannabis. Future evaluations of legalization should monitor: cannabis sales vol- umes, prices and content of tetrahydrocannabinol; prevalence and frequency of cannabis use among adolescents and adults in household and high school surveys; car crash fatalities and injuries involving drivers who are cannabis-impaired; emergency department presentations related to cannabis; the demand for treatment of cannabis use disorders; and the prevalence of regular cannabis use among vulnerable young people in mental health services, schools and the criminal justice system. Governments that propose to legalize and regulate cannabis use need to fund research to monitor the impacts of these policy changes on public health, and take advantage of this research to develop ways of regulating can­ nabis use that minimize adverse effects on public health.

Key words: Cannabis, legalization, recreational use, public health impacts, cannabis potency, cannabis-related harms, emergency department attendances, vulnerable young people

(World Psychiatry 2020;19:179–186)

Cannabis is globally the most widely some of the most liberal medical cannabis bis; c) it reduces the costs of policing the used illicit drug under international con- laws, Colorado and Washington State, in prohibition of cannabis use (freeing police trol. In 2017 it was estimated to be used by 20124. resources to address more serious crimes); 188 million adults (range 164-219 million) Combinations of arguments attracted and d) it enables governments to raise rev- worldwide or 3.8% of the global adult public support for recreational cannabis enue by taxing the sale of cannabis prod- population1. Cannabis use is more com- legalization in the US, as indicated by cit- ucts5. mon in North America and high-income izen-initiated referenda5. The first is that In principle, adult cannabis use could countries in Europe and Oceania2. Its use cannabis use is common among young be legalized in a range of different ways8. has increased in some low- and middle- adults and causes less harm than alcohol, Individuals could be allowed to grow can­ income countries, but remains low in tobacco and opioids6,7. The second is that nabis for their own use and gift it to others. Asia1. making cannabis use a criminal offence They could be allowed to form cannabis The inclusion of cannabis in the same causes more harm than cannabis use it- growers’ clubs that produce cannabis schedules of the international drug con- self, because some users are arrested and solely for their members’ use. The govern- trol treaties as heroin, cocaine and am- receive criminal records. The third is that ment could create a monopoly in cannabis phetamines has been controversial, and these criminal laws disproportionately production and sales in order to minimize public campaigns to legalize its use have affect cannabis users in minority popula- the promotion of cannabis use, as some been ongoing since the late 1960s3. The tions, such as African Americans and Lati- US states and Canadian provinces have route to legalization of adult use in the nos. The fourth is that legalization of adult done with alcohol. The government could US began with citizen-initiated referenda use is a better social policy than criminali- license non-profit cooperatives or chari- that legalized the medical use of cannabis, zation because: a) it eliminates the illicit table cooperatives that produce and sell initially for serious illnesses like cancer, market; b) it enables cannabis use to be cannabis without making a profit. Finally, but progressively under liberal regulations regulated to minimize adolescent access governments could allow the commer- that allowed the supply of cannabis by re- and protect adult cannabis consumers cialization of cannabis production and tail commercial cannabis “dispensaries”. – e.g., by controlling the tetrahydrocan- sale under a for-profit model like that These changes helped to reduce public nabinol (THC) content of cannabis prod- used for alcohol8. opposition to the legalization of adult can- ucts and reducing levels of contaminants Since 2012, eleven US states and the nabis use, which was first achieved by the – such as fungi, heavy metals and pesti- nation states Canada and Uruguay have passage of referenda in two states with cides – found in illicitly produced canna- passed legislation that has made it legal

World Psychiatry 19:2 - June 2020 179 for adults to produce, process and use can- nabis to registered users1. HOW HAS RECREATIONAL nabis. Nine US states, Uruguay and Cana- The Uruguayan model is still in the early LEGALIZATION AFFECTED da now permit legal retail cannabis sales as stage of implementation. So, it is difficult CANNABIS MARKETS IN THE US? well. In Washington DC and Vermont, it is to assess whether it has achieved its goals. legal for adults to grow cannabis for their Some have argued that the model is too re­ The legalization of recreational can- personal use and to give it to friends, but it strictive to undermine the illicit cannabis nabis use in the US has had a number of remains illegal to sell it8-10. market20,21. So far only 6,965 persons have effects. First, it has been followed by a sub- The creation of a legal cannabis market registered to grow their own cannabis and stantial decrease of the retail price of can- is more radical than the policy changes there are 115 cannabis clubs with 3,406 reg­ nabis17. Second, it has allowed adults to during the 1970s, which removed criminal istered members. Only 16 pharmacies (from obtain a regular supply of cannabis with- penalties or imprisonment for personal a total of 1,200) supply cannabis, and 34,696 out risk of criminal penalty. Third, it has use and possession, but left the supply of persons1 have registered to purchase can- produced a major diversification of the cannabis to the illicit market. Legalization nabis from pharmacies22. The total of 45,067 cannabis products for sale27. In addition permits the establishment of a legal canna- registered cannabis users comprise just to cannabis flower, cannabis retail outlets bis industry that has an interest in promot- under half the estimated number of can- also sell high-potency cannabis extracts ing cannabis use and, unlike policies that nabis users in Uruguay. We do not yet know (wax, shatter), edible cannabis (e.g., gum- legalize medical cannabis use, it allows what proportion of registered and unregis- my bears, candy and chocolates), and can- adults to use cannabis for any purpose. tered cannabis users still purchase cannabis nabis infused beverages17. These products Most US states that have legalized retail from the illicit market. presumably meet the needs of a broader cannabis sales have followed Colorado In October 2018, Canada became the range of adult consumers than the illicit and Washington State1 in using the same second nation to legalize the sale of canna- market primarily catered to, namely, daily regulatory approach as for alcohol, i.e. li- bis to adults23,24. The goals of legalization or near daily cannabis smokers17. The in- censing companies to produce and sell were to eliminate the illicit cannabis mar- creased availability and marketing of can- cannabis for a profit11,12. States differ in ket and regulate the production and sale nabis, and more publicly visible canna­­ whether they separately license growers, of cannabis to protect public health and bis use by adults, may make cannabis use processers, suppliers and retail sellers or minimize youth uptake25. The federal gov- more socially acceptable and enable more whether they allow licensees to perform all ernment licenses and regulates cannabis adults to use cannabis for a longer period of these roles (“vertical integration”)13,14. producers; advertising of cannabis is not of their lives than has been the case under All states have set the same minimum permitted; and cannabis products must be prohibition. legal purchase age for cannabis as for al- sold in plain packaging with health warn- Cannabis prices have fallen steeply in cohol, i.e. 21 years. Many have limited the ings. The minimum legal purchase age is the US states that have legalized its recre- quantity of cannabis that an adult can legal- 18 (unless a provincial government sets a ational use17,28,29. Prices no longer need to ly carry to 28.5 g15,16. In most states, canna- higher one), and it is an offence to drive include a premium to compensate illicit bis products are taxed on their sale price17, while impaired by cannabis. producers and sellers for the risks of being but tax rates vary between states1. Drug- Provincial governments in Canada reg- arrested or imprisoned or subjected to vi- impaired driving is an offence in all states ulate wholesale and retail cannabis sales olence by other illicit market participants. that have legalized cannabis (and in many in the same way as they regulate alcohol26. Legal cannabis production is no longer US states that have not), but states differ in Provinces with an alcohol retail monopo- small scale and clandestine, allowing how they have enforced this law13. ly can use the same regulatory approach growers to increase the scale of produc- In 2013, Uruguay became the first na- for cannabis, and retail cannabis sales are tion, reduce their costs, and pass these on tion to legalize adult cannabis use. It did allowed in provinces that licence for-prof- to consumers in the form of lower prices. so by allowing adults to use cannabis if it retailers of alcohol. The Canadian feder- If states allow licensees to grow, process they registered with the state and used al government collects taxes on cannabis and sell cannabis wholesale and retail, as one of three ways to obtain cannabis18: and shares these revenues with provincial in Colorado, then cannabis production they could grow their own cannabis, join governments. The sale of edible cannabis can become even more efficient29. a cannabis growers’ club that would pro- products and cannabis extracts began in Most US legalization states have im- duce enough cannabis for its members, or October 2019, with taxes based on their posed taxes on the retail price of cannabis purchase cannabis (produced under gov- THC content. products29. This method of taxing canna- ernment licence) from pharmacies19,20. As is the case with Uruguay, Canadian bis has had two consequences: state can- The policy was introduced in phases. In policy is still at an early stage of imple- nabis tax revenue has declined as retail the first, registered cannabis users were mentation. So, it is too early to evaluate its prices have fallen; and cannabis produc- allowed to grow their own cannabis. In impact. The remainder of this paper ac- ers and retailers have had an incentive the second, cannabis growers’ clubs were cordingly focuses on the impacts to date to increase the THC content per gram of licensed. In the third, a small number of of the legalization of recreational cannabis product to reduce prices and increase pharmacies were licensed to supply can- use in the US. profits29. Taxes may have contributed to

180 World Psychiatry 19:2 - June 2020 the increased sale of cannabis extracts legalize cannabis use. Moreover, the US dependence, i.e. more cannabis users will with a THC content of 70% or more (21% collects survey data on patterns of canna- experience impaired control over their of all sales in some states). The increase bis use in the population and health data cannabis use despite such use harming in cannabis potency presumably satisfies on cannabis- and alcohol-related harms. them43. The 9% risk of dependence among the preferences of daily cannabis users As Canada and Uruguay proceed to im- lifetime users in the US in the early 1990s (who account for most sales). A cap on plement cannabis legalization, similar may increase in those who use more po- THC content or a minimum unit price or high quality survey33,34 and other data will tent cannabis products44. tax based on THC content would reduce be collected to assess the public health Daily cannabis users have impaired co­ this incentive8, but so far no US state has impacts of legalization in these countries. gnitive performance that appears to be re- adopted any of these policies. versed by abstinence45. Adolescents and Cannabis prices may decline further. young adults who are regularly intoxicat- ­Lo­cal regulations have restricted up to now WHAT ADVERSE HEALTH ed during their schooling have poorer ed- the number and location of retail outlets in EFFECTS MAY INCREASE AFTER ucational attainment46. Cannabis-related some states to the larger cities30. Cannabis CANNABIS LEGALIZATION? cognitive impairment may also occur in prices are likely to fall much further if legal- older adults who regularly use cannabis ization of adult use becomes US national We summarize here the adverse effects for recreational purposes47. policy, because this would allow cannabis that may increase if harmful patterns of Daily cannabis use is associated with an production on a larger scale, potentially per­ cannabis use, especially daily use, increase increased risk of psychotic symptoms or a mit the establishment of inter-state com- as a result of legalization. The content is diagnosis of a schizophreniform psycho- merce, facilitate the increase in multi-state based on reviews of the evidence on the sis in prospective epidemiological stud- operations, allow the development of US- adverse health effects of cannabis35-37 and ies48,49. These risks are higher in those who based multinational companies via merg- analyses of health outcomes that should begin cannabis use in adolescence, those ers and acquisitions, and attract large scale be monitored after cannabis legalization who use it more often and for longer48, and investment from the alcohol, tobacco and 38-40. those who use strains with high THC and/ finance industries. or low cannabidiol50. Psychotic symptoms Historical experiences with the regula- occur two years earlier on average in regu- tion of alcohol and tobacco31,32 suggest Acute effects lar cannabis users51, and persons with a that, in the short term, increasing access to psychosis who continue to use cannabis more potent cannabis products at a lower Car accidents may increase if more can- have more frequent episodes and longer price is likely to increase the frequency of nabis users drive, or drive more often, while periods of hospitalization for their illness- cannabis use among current users. In the impaired, or if cannabis users who drive es52. In major European cities, an associa- longer term, a profit-seeking legal canna- use more potent cannabis products36,37. tion has been reported between average bis industry is likely to attempt to increase More cannabis users may present to emer- cannabis potency and the incidence of the number of cannabis users, and the reg- gency departments with acute psychologi- psychosis53. ularity of their use, in order to maximize its cal distress and psychotic symptoms if they Heavy cannabis users can develop a profits. This will involve a combination of use more potent cannabis products such hyperemesis syndrome54, with severe ab- promotional activities (e.g., media adver- as extracts36. Adverse effects of cannabis on dominal pain and cyclical vomiting. The tising, price discounts, and discounts for fetal development36,37 may increase if more syndrome is most often reported by daily regular purchasers) that aim to increase women use cannabis during pregnancy, as cannabis users in the absence of any other the number of daily cannabis users and appears to be the case in the US41. medical cause55. It is relieved by hot bath- the proportion of adults who use cannabis. Relationships between cannabis use ing56, resolves when users abstain from There is considerable uncertainty about and the use of alcohol, tobacco and opioids using cannabis, and may recur if they re- how much and how soon such promotion- will substantially affect the public health start cannabis54. A small number of deaths al activities will succeed. Experience with impacts of cannabis legalization38,40,42. The have been attributed to complications of alcohol suggests, however, that the larger public health burdens of these drugs could this syndrome57. the proportion of the population that uses be reduced if cannabis becomes a substi- Case series and a case-control study58 cannabis, and the more often they do so, tute, while their impact could be amplified suggest that heavy cannabis smoking may the larger will be any adverse public health if there is more concurrent use of cannabis increase cardiovascular disease risk in impacts of cannabis legalization31. and these drugs38,40. young heavy cannabis smokers59-61. Mid- In the remainder of this paper, we re- dle-aged men who have had a myocardial view evidence on the public health effects infarction may experience angina if they to date of the legalization of recreational Chronic effects smoke cannabis62, and are at increased cannabis use in the US. As an early adop- risk of a recurrence if they are cannabis ter, the US is likely to influence the policies More frequent use of potent cannabis users63-65. adopted in other countries that decide to may increase the prevalence of cannabis Cannabis-only smokers report more

World Psychiatry 19:2 - June 2020 181 cough, sputum and wheezing than per- frequency of use among adult cannabis zation in Colorado there have also been sons who do not smoke cannabis66-71, and users in US states that have legalized rec- increases in hospitalizations for cannabis these symptoms remit if they quit72. How- reational cannabis78,81,82. Surveys in Colo- abuse and dependence89, motor vehicle ever, cannabis smokers do not appear to rado and Washington State have found accidents and injuries related to cannabis be at higher risk of chronic obstructive pul- mixed evidence on the impacts of can- abuse90, and head injuries attributed to an monary disease72,73. nabis legalization on adolescent cannabis increase in falls91. Systematic reviews have not found an use. There was an increase in cannabis An increase in emergency department association between cannabis use and use among students after legalization in presentations for hyperemesis in Aurora, head or neck cancer74, or lung cancer75. By Washington State, but a decrease among Colorado was reported after medical can- contrast, a meta-analysis of three studies76 adolescents in Colorado83,84. No changes nabis use was legalized in 2000, and a fur­ found a small increase in risk of testicular in cannabis use were reported among ther increase after recreational use legali- cancer among high-frequency cannabis youth in two surveys in Washington State zation92. A 46% increase in the incidence users and in those who had used cannabis conducted the year before and the year of cyclic vomiting was reported between for ten or more years. after legalization of recreational use was 2010 and 2014 in the Colorado State Inpa- implemented84. Darnell and Bitney85 did tient Database93. not find changes in youth cannabis use in An increase in cannabis-related emer- HEALTH EFFECTS OF Washington State between 2002 and 2016. gency department presentations has LEGALIZING RECREATIONAL Anderson et al86 failed to find an increase been reported after legalization in Boul- CANNABIS USE IN THE US in youth cannabis use in the Youth Risk der, Colorado for childhood poisonings, Behavior Surveys in the four years before psychological distress in adults, severe State level legalization of recreational and the three years after the legalization vomiting, and severe burns in users who cannabis use for adults was only imple- of recreational use. Dilley et al87 reported had attempted to extract THC from can- mented about five years ago in Washington very similar results in analyses of Youth nabis oils using butane94. State and Colorado, the US jurisdictions Risk Behaviour Surveys in Washington Calcaterra et al95 analyzed trends in can- with the longest experience of a legal re- State. nabis- and alcohol-related presentations to gime to date. This is probably too short a Cerdá et al81 recently compared trends a hospital network in Colorado that provid- period to judge the full effects of legaliza- in regular past 30 day cannabis use and ed emergency medical care to low-income tion. It has taken time to produce depend- cannabis use disorders among adoles- patients in two periods: January 2009 to able supplies of cannabis within states cents and young adults in US states that December 2013 and January 2014 to De- that have legalized, and there are a limited have and have not legalized recreational cember 2015. The rate of cannabis-related number of retail outlets available in a rela- cannabis use, using data from the US drug presentations increased steeply in the lat- tively small number of locations in these household survey, the National Survey on ter period, while presentations involving states1. For these reasons, evaluations of Drug Use and Health. They found sugges- alcohol were unchanged. Cannabis-related the first five or so years after legalization tive evidence of a small increase in these presentations were more likely to involve may provide a poor indication of the im- outcomes among 12-17 year olds, but did younger adults and more likely to lead to pacts of cannabis use on public health not find any similar effects among those hospitalization, especially for psychiatric when the industry develops over a decade aged 18-25 years. They were cautious in care. or more42,77. interpreting the former, because they es- In Colorado, emergency department pres­ timated that the small increases could be entations for mental illness with a canna- due to unmeasured confounders. This bis-related code increased five times faster Effects on cannabis use was a less plausible explanation for simi- than mental illness presentations without lar increases observed in regular cannabis such a code between 2012 and 201488. The If experience with alcohol and tobacco use and cannabis use disorders among largest increases were for persons who re­ is a reasonable guide, we would expect de- adults 26 years and older81. ceived diagnoses of schizophrenia and oth­er clines in cannabis prices to be followed by psychotic disorders, suicide and intentional increases in the frequency of use among self-harm, and mood disorders96. existing users31,32,78. There is some evi- Effects on cannabis-related A review of pediatric cases from 1975 dence of increased frequency of use in re- hospitalizations to 2015 found more unintentional canna- sponse to the relatively small declines in bis ingestion by children in US states that cannabis prices that occurred under pro- Cannabis-related hospitalizations have had legalized medical and recreational hibition79. It is more difficult to estimate increased in Colorado after recreational cannabis use97. This increase prompted how much cannabis use may increase when cannabis use was legalized. These increas- limits on package and serving sizes of ed- cannabis prices fall by 30-50%80. es have been in addition to earlier increases ible cannabis products in 201798. Despite Household survey data suggest that that occurred after the legalization of medi- these changes, pediatric hospital visits lower cannabis prices have increased the cal cannabis use88. After cannabis legali- and calls to poison centres for cannabis

182 World Psychiatry 19:2 - June 2020 ingestion increased after 2017. Similar MONITORING THE FUTURE Treatment seeking for cannabis depen­ increases in accidental poisoning among PUBLIC HEALTH IMPACT OF dence should also be monitored. It is un- children and adolescents were reported CANNABIS LEGALIZATION certain how legalization may affect it. One in Massachusetts before and after the would expect a decline in treatment seek- legalization of medical cannabis use, de- There are a number of reasons why the ing among adult cannabis users who will spite the use of child-proof packaging and effects of cannabis legalization to date may no longer be legally coerced into treat- warning labels99. underestimate its full impacts on public ment as an alternative to imprisonment. health in the longer term. Adolescents with cannabis use problems First, the commercialization of the can- may still be arrested107 and coerced into Effects on road crashes nabis industry is incomplete in the US. treatment, and their numbers may in- While cannabis remains prohibited under crease if courts use treatment as an alter- Studies of the effects of cannabis legali- US federal law, there are also prohibitions native to their criminal prosecution if they zation on traffic accidents have produced on inter-state commerce in cannabis and are caught using cannabis. mixed findings. investment by the alcohol, tobacco and Legalization may also reduce treatment Chung et al100 reported an increase in finance industries. It is difficult for canna- seeking among persons with cannabis prob­ the rate of patients admitted to Colorado bis businesses to use banks or to advertise lems if increased access to legal and cheap hospitals for traumatic injury who were cannabis, because it remains an illegal cannabis products reduces the economic cannabis-positive between 2012 and 2015, commodity. National cannabis legaliza- costs of cannabis use and social pressure in the absence of any corresponding in- tion would remove these constraints and from families and friends to stop using can- crease in neighbouring states that had not allow the full commercialization of the nabis. On the other hand, legalization of legalized cannabis. cannabis industry under constitutional adult use may reduce the stigma attached However, Aydelotte et al101 did not find protections including the “commercial to problem cannabis use and thereby en- greater changes in traffic fatality rates in freedom of speech”. courage earlier treatment seeking, e.g. if Washington State and Colorado using Fa- Second, it is too soon to evaluate the ef- education campaigns increase public rec- tality Analysis Reporting System (FARS) fects of cannabis legalization in Canada ognition of cannabis use disorders and en- data than in neighbouring states that had and Uruguay. Both countries are still imple- courage users to seek treatment. not legalized cannabis. Sevigny102 ana- menting their models, so it will take time The US national treatment data108 will lyzed FARS data (1993-2014) using data for legalization to become fully operation- provide useful information on these trends. imputation to address the large amount of al. These data could be expanded to include missing data, and did not find an impact Third, even after legalization is fully im- information from new treatment entrants of legalization on cannabis-positive driv- plemented, one would expect a delay be- on: reasons for seeking treatment; the type ing among people involved in a fatal crash. tween any increases in cannabis use and and amounts of cannabis used; usual routes Lane and Hall103 found a short-term in- the detection of increased problems re- of administration; and where they obtained crease in traffic fatalities in both US states lated to regular cannabis use in the health their cannabis (to assess how many prob- that had legalized the commercial sale of care system. The following section discuss- lem users are still using the illicit market). cannabis (i.e., Colorado, Washington State es indicators that should be monitored to A major research priority should be to and Oregon) and their neighbouring juris- evaluate the longer-term public health im- improve assessments of the role that can- dictions. pacts of cannabis legalization. nabis-impaired driving plays in fatal motor vehicle accidents. This research should as- sess the degree to which cannabis is a sub- Treatment seeking for cannabis use Potential indicators of future stitute for alcohol among young men, and disorders cannabis-related harm the extent to which it reduces other types of alcohol-related harm, such as suicides Darnell and Bitney85 compared trends Studies of the public health impacts of and assaults. in treatment seeking for cannabis use dis- legalization should monitor trends in acute It will be important to monitor any ef- orders in the Treatment Episode Data Set harms that are likely to increase if more fects that cannabis legalization has on to- in Washington State in the first two years adults use more potent cannabis prod- bacco smoking and alcohol use among after legalization with trends in a synthet- ucts more often. These include: car crash adolescents and young adults. With the ic cohort comprising a weighted sample fatalities and injuries involving cannabis- decline in youth tobacco use, suggestive of other US states that had not legalized impaired drivers; emergency department evidence has emerged of a “reverse gate- cannabis. Treatment demand declined in attendances for myocardial infarctions, way effect”, in which initiation of cannabis Washington State after legalization, but at acute coronary syndromes and strokes in smoking has increased tobacco smoking the same rate as it declined in states that young adults58,104-106, and cyclic vomiting among young adults109. had not legalized cannabis. in young adults. The social distributional effects of can-

World Psychiatry 19:2 - June 2020 183 nabis legalization should also be examin­ motor vehicle crashes are inconsistent. lated harm after legalization. These may ed. One major motivation for cannabis le­ There are limited data on the impacts on include: tighter regulation of youth ac- galization has been to eliminate the un- treatment seeking for cannabis use dis­ cess to cannabis; using taxes to discour- equal enforcement of criminal penalties orders. age heavy cannabis use (e.g., by setting against minority cannabis users. Legaliza- It would be unwise to assume that the minimum prices for cannabis products, tion has reduced arrests, but it is too early modest effects of cannabis legalization imposing potency caps, and basing can- to assess its impact on rates of incarcera- observed to date will predict its longer- nabis taxes on THC content115); consum- tion and minority differentials in imprison- term effects. The legalization of cannabis er-tested health warnings about the risks ment. It will also be important to see if mi- markets has already substantially reduced of cannabis use, especially daily cannabis norities are over-represented among prob- the price of cannabis and increased its use, such as cognitive impairment and can­ lem cannabis users who seek treatment110. potency, and prices are likely to fall fur- nabis dependence; and research to de- Research should also monitor any ad- ther if legalization becomes national pol- velop more effective ways of discouraging verse health effects that cannabis legali- icy in the US. Legalization on the limited adolescents from starting cannabis use116. zation has on cannabis users over the age scale to date has increased regular can- of 50. US surveys report an increase in nabis use among adults and it may have use among this age group since legaliza- increased cannabis use disorders among ACKNOWLEDGEMENTS 111,112 tion , probably for a combination of adult users, although the evidence on this The authors would like to thank S. Yeates for her assis- medical and quasi-medical reasons (e.g., issue is insufficient. In the longer term, tance in searching the popular and scientific literature and in preparing this paper for publication. to assist with sleep, control pain, stimulate experience with alcohol suggests that appetite). Older users may be at higher more liberal regulation that provides legal risk of some adverse health effects, such access to cheaper, more potent canna- REFERENCES as car crashes, cardiovascular disease and bis products will increase the number of cognitive impairment. regular users and probably the number of 1. United Nations Office on Drugs and Crime. World drug report 2019. Vienna: United Nations, We need more rigorous evaluations of new cannabis users. There is considerable 2019. the public health impacts of cannabis le- uncertainty about by how many and how 2. Peacock A, Leung J, Larney S et al. Global sta- galization42. Comparisons of differences soon this may occur. tistics on alcohol, tobacco and illicit drug use: 2017 status report. Addiction 2018;113:1905-26. between states in time series data on vari- Future evaluations of the public health 3. Room R, Fischer B, Hall WD et al. Cannabis pol- ous causes of hospitalization and death impacts of cannabis legalization should icy: moving beyond stalemate. Oxford: Oxford are of limited value because they are not assess its effects on: attitudes towards can- University Press, 2010. 4. Kilmer B, MacCoun RJ. How medical marijuana able to test alternative explanations of nabis use in young people; the frequency smoothed the transition to marijuana legaliza- 77 state level differences . We also need of cannabis use in high-risk youth and tion in the United States. Annu Rev Law Soc Sci large prospective studies of the effects of young adults (e.g., those who seek help for 2017;13:181-202. 5. Felson J, Adamczyk A, Thomas C. How and these policy changes on the use of canna- mental health problems and those in the why have attitudes about cannabis legalization bis and other drugs and their impact on criminal justice system); cannabis-related changed so much? Soc Sci Res 2019;78:12-27. health outcomes in individuals42. car crashes and emergency department 6. Degenhardt L, Whiteford HA, Ferrari AJ et al. Global burden of disease attributable to illicit attendances for cannabis-related prob- drug use and dependence: findings from the lems; treatment seeking for cannabis use Global Burden of Disease Study 2010. Lancet CONCLUSIONS disorders and its outcomes; and persons 2013;382:1564-74. 7. Global Burden of Disease 2016 Risk Factors seeking treatment for mental disorders. ­Collaborators.­ Global, regional, and national The legalization of recreational canna­ Research should also assess how legal- comparative risk assessment of 84 behavioural, bis use in Canada, Uruguay and an increa­ ization affects the use and harms of alco- environmental and occupational, and metabol- ic risks or clusters of risks, 1990-2016: a system- sing number of states in the US is a large hol and tobacco and other drug use (e.g., atic analysis for the Global Burden of Disease scale policy experiment whose effects may opioids) among youth and young and Study 2016. Lancet 2017;390:1345-422. not be known for a decade or more. So far older adults. In the longer term we need 8. Caulkins J, Kilmer B, Kleiman M et al. Consider- ing marijuana legalization: insights for Vermont legalization has not produced large in­ to assess the effects of legalization on the and other jurisdictions. Santa Monica: RAND creases in cannabis use among youth in the duration of cannabis use in adulthood, Corporation, 2015. US. As expected, it has increased regular because it is likely that legalization will ex- 9. Garvey T, Yeh BT. State legalization of recrea- tional marijuana: selected legal issues. Wash- cannabis use among adult users. It has also tend the duration of cannabis use beyond ington: Congressional Research Office, 2014. increased acute cannabis-related presenta- the late 20s, the age at which most users 10. US Government Accountability Office. State tions to emergency departments in adults desisted under prohibition113. There is marijuana legalization, DOJ should document its approach to monitoring the effects of legali- and children for physical and mental health some suggestive evidence that the dura- zation. Washington: US Government Account- problems related to cannabis use (e.g., psy- tion of cannabis use has already increased ability Office, 2015. chological distress, vomiting syndromes, among recent birth cohorts114. 11. Hall WD. Alcohol and cannabis: comparing their adverse health effects and regulatory re- and accidental poisonings in children). These evaluations should inform the gimes. Int J Drug Policy 2017;42:57-62. Studies of the effects of the legalization on design of policies to reduce cannabis-re- 12. Room R. Legalizing a market for cannabis for

184 World Psychiatry 19:2 - June 2020 pleasure: Colorado, Washington, Uruguay and alence of cannabis use and related metrics in try 2015;2:233-8. beyond. Addiction 2014;109:345-51. Canada. Ottawa: Government of Canada, 2019. 51. Large M, Sharma S, Compton MT et al. Canna- 13. Pardo B. Cannabis policy reforms in the Amer­ 34. Statistics Canada. National cannabis survey, bis use and earlier onset of psychosis: a system- icas: a comparative analysis of Colorado, Wash­ first quarter 2019. Ottawa: Government of Can- atic meta-analysis. Arch Gen Psychiatry 2011; ington, and Uruguay. Int J Drug Policy 2014;25: ada, 2019. 68:555-61. 727-35. 35. Babor T, Caulkins JP, Fischer B et al. Drug policy 52. Schoeler T, Monk A, Sami MB et al. Continued 14. Wallach PA, Hudak J. Legal marijuana: com- and the public good, 2nd ed. New York: Oxford versus discontinued cannabis use in patients paring Washington and Colorado. Washington: University Press, 2018. with psychosis: a systematic review and meta- Brookings Institution, 2014. 36. Hall WD, Renström M, Poznyak V. The health analysis. Lancet Psychiatry 2016;3:215-25. 15. Quinn S. Alaska allows recreational marijuana and social effects of nonmedical cannabis use. 53. Di Forti M, Quattrone D, Freeman TP et al. The as legalization campaign spreads. Reuters, Feb- Geneva: World Health Organization, 2016. contribution of cannabis use to variation in the ruary 24, 2015. 37. National Academies of Sciences Engineering incidence of psychotic disorder across Europe 16. Wallach PA. Washington’s marijuana legaliza- and Medicine. The health effects of cannabis (EU-GEI): a multicentre case-control study. tion grows knowledge, not just pot. Washing- and cannabinoids: the current state of evidence Lancet Psychiatry 2019;6:427-36. ton: Brookings Institution and the Washington and recommendations for research. Washing- 54. Allen JH, de Moore GM, Heddle R et al. Can­ Office on Latin America, 2014. ton: National Academies Press for the National nabinoid hyperemesis: cyclical hyperemesis in 17. Smart R, Caulkins JP, Kilmer B et al. Variation Academies of Sciences Engineering and Medi- association with chronic cannabis abuse. Gut in cannabis potency and prices in a newly legal cine, 2017. 2004;53:1566-70. market: evidence from 30 million cannabis sales 38. Fischer B, Russell C, Rehm J et al. Assessing the 55. Simonetto DA, Oxentenko AS, Herman ML et al. in Washington state. Addiction 2017;112:2167- public health impact of cannabis legalization in Cannabinoid hyperemesis: a case series of 98 77. Canada: core outcome indicators towards an patients. Mayo Clin Proc 2012;87:114-9. 18. Hudak J, Ramsey G, Walsh J. Uruguay’s canna- ‘index’ for monitoring and evaluation. J Public 56. Khattar N, Routsolias JC. Emergency depart- bis law: pioneering a new paradigm. Washing- Health 2019;41:412-21. ment treatment of cannabinoid hyperemesis ton: Center for Effective Public Management at 39. Hall WD, Lynskey M. Evaluating the public syndrome: a review. Am J Ther 2018;25:e357-61. Brookings, 2018. health impacts of legalizing recreational canna- 57. Nourbakhsh M, Miller A, Gofton J et al. Can- 19. Cerdá M, Kilmer B. Uruguay’s middle-ground bis use in the United States. Addiction 2016;111: nabinoid hyperemesis syndrome: reports of approach to cannabis legalization. Int J Drug 1764-73. fatal cases. J Forensic Sci 2019;64:270-4. Policy 2017;42:118-20. 40. Windle SB, Wade K, Filion KB et al. Potential 58. Jouanjus E, Lapeyre-Mestre M, Micallef J. Can- 20. Walsh J, Ramsey G. Cannabis regulation in harms from legalization of recreational cannabis nabis use: signal of increasing risk of serious Uruguay: an innovative law facing major chal- use in Canada. Can J Public Health 2019;110:222- cardiovascular disorders. J Am Heart Assoc 2014; lenges. J Drug Policy Anal 2016;11. 6. 3:e000638. 21. Ramsey G. Getting regulation right: assessing 41. Volkow ND, Han B, Compton WM et al. Self-re- 59. Arora S, Goyal H, Aggarwal P et al. ST-segment Uruguay’s historic cannabis initiative. Wash- ported medical and nonmedical cannabis use elevation myocardial infarction in a 37-year-old ington: WOLA Advocacy for Human Rights in among pregnant women in the United States. man with normal coronaries – it is not always the Americas, 2016. JAMA 2019;322:167-9. cocaine! Am J Emerg Med 2012;30:2091.e3-5. 22. Instituto de Regulacion y Control de Cannabis. 42. Choo EK, Emery SL. Clearing the haze: the com- 60. Casier I, Vanduynhoven P, Haine S et al. Is re- Mercado regulado de cannabis informe VII al plexities and challenges of research on state cent cannabis use associated with acute coro- 30/06/19. Montevideo: Instituto de Regulacion mari­juana laws. Ann NY Acad Sci 2017;1394:55- nary syndromes? An illustrative case series. y Control de Cannabis, 2019. 73. Acta Cardiol 2014;69:131-6. 23. Cox C. The Canadian Cannabis Act legalizes 43. Budney AJ, Sofis MJ, Borodovsky JT. An update 61. Hodcroft CJ, Rossiter MC, Buch AN. Cannabis- and regulates recreational cannabis use in 2018. on cannabis use disorder with comment on associated myocardial infarction in a young Health Policy 2018;122:205-9. the impact of policy related to therapeutic and man with normal coronary arteries. J Emerg 24. Government of Canada. Cannabis Act (S.C. 2018, recreational cannabis use. Eur Arch Psychiatry Med 2014;47:277-81. c. 16). Ottawa: Department of Justice, 2018. Clin Neurosci 2019;269:73-86. 62. Aronow W, Cassidy J. Effect of marihuana and 25. Government of Canada. Cannabis legalization 44. Freeman TP, Winstock AR. Examining the pro- placebo marihuana smoking on angina pecto- and regulation: cannabis is now legal. Ottawa: file of high-potency cannabis and its association ris. N Engl J Med 1974;291:65-7. Department of Justice, 2018. with severity of cannabis dependence. Psychol 63. Mittleman MA, Lewis R, Maclure M et al. Trig- 26. Watson TM, Hyshka E, Bonato S et al. Early-stage Med 2015;45:3181-9. gering myocardial infarction by marijuana. Cir- cannabis regulatory policy planning across Can- 45. Scott JC, Slomiak ST, Jones JD et al. Association culation 2001;103:2805-9. ada’s four largest provinces: a descriptive over- of cannabis with cognitive functioning in ado- 64. Mukamal K, Maclure M, Muller J et al. An ex- view. Subst Use Misuse 2019;54:1691-704. lescents and young adults: a systematic review ploratory prospective study of marijuana use 27. Spindle TR, Bonn-Miller MO, Vandrey R. Chang­ and meta-analysis. JAMA Psychiatry 2018;75: and mortality following acute myocardial in- ing landscape of cannabis: novel products, for- 585-95. farction. Am Heart J 2008;155:465-70. mulations, and methods of administration. Curr 46. Horwood L, Fergusson D, Hayatbakhsh M et al. 65. Frost L, Mostofsky E, Rosenbloom JI et al. Mari- Opin Psychol 2019;30:98-102. Cannabis use and educational achievement: juana use and long-term mortality among sur- 28. Swanson A, Gamio L. How the price of pot dif- findings from three Australasian cohort studies. vivors of acute myocardial infarction. Am Heart fers in 50 states and 8 major cities. Washington Drug Alcohol Depend 2010;110:247-53. J 2013;165:170-5. Post, June 22, 2015. 47. Auer R, Vittinghoff E, Yaffe K et al. Association 66. Aldington S, Williams M, Nowitz M et al. Effects 29. Caulkins JP, Hawken A, Kilmer B et al. Marijua- between lifetime marijuana use and cognitive of cannabis on pulmonary structure, function na legalization: what everyone needs to know. function in middle age: the Coronary Artery and symptoms. Thorax 2007;62:1058-63. New York: Oxford University Press, 2012. Risk Development in Young Adults (CARDIA) 67. Bloom J, Kaltenborn W, Paoletti P et al. Res- 30. Subritzky T, Pettigrew S, Lenton S. Issues in the Study. JAMA Intern Med 2016;176:352-61. piratory effects of non-tobacco cigarettes. BMJ implementation and evolution of the commer- 48. Marconi A, Di Forti M, Lewis CM et al. Meta- 1987;295:1516-8. cial recreational cannabis market in Colorado. analysis of the association between the level of 68. Moore BA, Augustson EM, Moser RP et al. Res- Int J Drug Policy 2016;27:1-12. cannabis use and risk of psychosis. Schizophr piratory effects of marijuana and tobacco use in 31. Babor T, Caetano R, Casswell S et al. Alcohol: no Bull 2016;42:1262-9. a U.S. sample. J Gen Intern Med 2005;20:33-7. ordinary commodity: research and public policy, 49. Gage SH, Hickman M, Zammit S. Association 69. Tan WC, Lo C, Jong A et al. Marijuana and 2nd ed. Oxford: Oxford University Press, 2010. between cannabis and psychosis: epidemio- chronic obstructive lung disease: a population- 32. Chaloupka FJ, Warner KE. The economics of logic evidence. Biol Psychiatry 2016;79:549-56. based study. Can Med Assoc J 2009;180:814-20. smoking. In: Newhouse JP, Cuyler AJ (eds). The 50. Di Forti M, Marconi A, Carra E et al. Proportion 70. Tashkin DP, Coulson AH, Clark VA et al. Respira­ handbook of health economics. New York: El- of patients in south London with first-episode tory symptoms and lung function in habitual sevier, 2000:1539-627. psychosis attributable to use of high potency heavy smokers of marijuana alone, smokers of 33. Statistics Canada. Analysis of trends in the prev- cannabis: a case-control study. Lancet Psychia- marijuana and tobacco, smokers of tobacco

World Psychiatry 19:2 - June 2020 185 a­lone, and non-smokers. Am Rev Respir Dis use: new estimates from the Youth Risk Behav- Prev 2018;118:57-65. 1987;135:209-16. ior Surveys. JAMA Pediatr 2019;173:879-81. 103. Lane TJ, Hall W. Traffic fatalities within US 71. Taylor DR, Poulton R, Moffitt T et al. The respir- 87. Dilley JA, Richardson SM, Kilmer B et al. Preva- states that have legalized recreational canna- atory effects of cannabis dependence in young lence of cannabis use in youths after legaliza­ ­ bis sales and their neighbours. Addiction 2019; adults. Addiction 2000;95:1669-77. tion in Washington State. JAMA Pediatr 2019; 114:847-56. 72. Hancox RJ, Shin HH, Gray AR et al. Effects of 173:192-3. 104. Jouanjus E, Leymarie F, Tubery M et al. Can- quitting cannabis on respiratory symptoms. Eur 88. Wang GS, Hall K, Vigil D et al. Marijuana and nabis-related hospitalizations: unexpected Respir J 2015;46:80-7. acute health care contacts in Colorado. Prev Med serious events identified through hospital data- 73. Kempker JA, Honig EG, Martin GS. The effects 2017;104:24-30. bases. Br J Clin Pharmacol 2011;71:758-65. of marijuana exposure on expiratory airflow. A 89. Davis JM, Mendelson B, Berkes JJ et al. Public 105. Wolff V, Armspach JP, Lauer V et al. Ischaemic study of adults who participated in the U.S. Na- health effects of medical marijuana legalization strokes with reversible vasoconstriction and tional Health and Nutrition Examination Study. in Colorado. Am J Prev Med 2016;50:373-9. without thunderclap headache: a variant of the Ann Am Thorac Soc 2015;12:135-41. 90. Delling FN, Vittinghoff E, Dewland TA et al. reversible cerebral vasoconstriction syndrome? 74. Berthiller J, Straif K, Boniol M et al. Canna- Does cannabis legalisation change healthcare Cerebrovasc Dis 2015;39:31-8. bis smoking and risk of lung cancer in men: a utilisation? A population-based study using the 106. Wolff V, Lauer V, Rouyer O et al. Cannabis use, pooled analysis of three studies in Maghreb. J healthcare cost and utilisation project in Colo- ischemic stroke, and multifocal intracranial Thorac Oncol 2008;3:1398-403. rado, USA. BMJ Open 2019;9:e027432. vasoconstriction: a prospective study in 48 con- 75. Zhang LR, Morgenstern H, Greenland S et al. 91. Sokoya M, Eagles J, Okland T et al. Patterns of secutive young patients. Stroke 2011;42:1778-80. Cannabis smoking and lung cancer risk: pooled facial trauma before and after legalization of 107. Plunk AD, Peglow SL, Harrell PT et al. Youth analysis in the International Lung Cancer Con- marijuana in Denver, Colorado: a joint study be- and adult arrests for cannabis possession after sortium. Int J Cancer 2015;136:894-903. tween two Denver hospitals. Am J Emerg Med decriminalization and legalization of cannabis. 76. Gurney J, Shaw C, Stanley J et al. Cannabis expo- 2018;36:780-3. JAMA Pediatr 2019;173:763-9. sure and risk of testicular cancer: a systematic 92. Heard K, Monte AA, Hoyte CO. Brief commen- 108. US Substance Abuse and Mental Health Ser- review and meta-analysis. BMC Cancer 2015;15: tary: consequences of marijuana – observa- vices Administration. N-SSATS quick statistics 897. tions from the emergency department. Ann state profiles. Rockville: Substance Abuse and 77. Smart R, Pacula RL. Early evidence of the im- Intern Med 2019;170:124. Mental Health Services Administration, Center pact of cannabis legalization on cannabis use, 93. Bhandari S, Jha P, Lisdahl KM et al. Recent for Behavioral Health Statistics and Quality, cannabis use disorder, and the use of other sub- trends in cyclic vomiting syndrome-associated 2015. stances: findings from state policy evaluations. hospitalisations with liberalisation of cannabis 109. Becker J, Schaub MP, Gmel G et al. Cannabis Am J Drug Alcohol Abuse 2019;45:644-63. use in the state of Colorado. Intern Med J 2019; use and other predictors of the onset of daily 78. Pacula RL, Kilmer B, Wagenaar AC et al. Devel- 49:649-55. cigarette use in young men: what matters most? oping public health regulations for marijuana: 94. Monte AA, Zane RD, Heard KJ. The implica- Results from a longitudinal study. BMC Public lessons from alcohol and tobacco. Am J Public tions of marijuana legalization in Colorado. Health 2015;15:1-10. Health 2014;104:1021-8. JAMA 2015;313:241-2. 110. Males M, Buchen L. Reforming marijuana laws: 79. Pacula RL. Examining the impact of marijuana 95. Calcaterra SL, Hopfer CJ, Keniston A et al. Changes which approach best reduces the harms of crim- legalization on marijuana consumption: in- in healthcare encounter rates possibly related inalization? A five state analysis. San Francisco: sights from the economics literature. Santa to cannabis or alcohol following legalization of Centre on Juvenile and Criminal Justice, 2014. Monica: RAND Corporation, 2010. recreational marijuana in a safety-net hospital: 111. Black P, Joseph LJ. Still dazed and confused: 80. Kilmer B, Caulkins JP, Pacula RL et al. Altered an interrupted time series analysis. J Addict Med midlife marijuana use by the baby boom gen- state? Assessing how marijuana legalization 2019;13:201-8. eration. Deviant Behav 2014;35:822-41. in California could influence marijuana con- 96. Hall KE, Monte AA, Chang T et al. Mental 112. Han BH, Sherman S, Mauro PM et al. Demo- sumption and public budgets. Santa Monica: health-related emergency department visits graphic trends among older cannabis users in the RAND Drug Policy Research Center, 2010. associated with cannabis in Colorado. Acad United States, 2006-13. Addiction 2017;112:516- 81. Cerdá M, Mauro C, Hamilton A et al. Association Emerg Med 2018;25:526-37. 25. between recreational marijuana legalization in 97. Richards JR, Smith NE, Moulin AK. Uninten- 113. Bachman J, Wadsworth K, O’Malley P et al. the United States and changes in marijuana use tional cannabis ingestion in children: a system- Smoking, drinking, and drug use in young adult­ and cannabis use disorder from 2008 to 2016. atic review. J Pediatr 2017;190:142-52. hood: the impacts of new freedoms and new JAMA Psychiatry 2020;77:165-71. 98. Koski L. Retail marijuana product manufactur­ responsibilities. Mahwah: Lawrence Erlbaum, 82. Everson EM, Dilley JA, Maher JE et al. Post-le- ing, packaging, and labeling compliance guid­ 1997. galization opening of retail cannabis stores and ance. Lakewood: Marijuana Enforcement Di­ 114. Terry-McElrath YM, Patrick ME, O’Malley PM adult cannabis use in Washington State, 2009- vision, 2017. et al. The end of convergence in developmental 2016. Am J Public Health 2019;109:1294-301. 99. Whitehill JM, Harrington C, Lang CJ et al. Inci- patterns of frequent marijuana use from ages 18 83. Cerdá M, Wall M, Feng T et al. Association of dence of pediatric cannabis exposure among to 30: an analysis of cohort change from 1976- state recreational marijuana laws with adoles- children and teenagers aged 0 to 19 years be- 2016. Drug Alcohol Depend 2018;191:203-9. cent marijuana use. JAMA Pediatr 2017;171: fore and after medical marijuana legalization 115. Shover CL, Humphreys K. Six policy lessons 142-9. in Massachusetts. JAMA Netw Open 2019;2: relevant to cannabis legalization. Am J Drug 84. Kerr WC, Ye Y, Subbaraman MS et al. Changes e199456. Alcohol Abuse 2019;45:698-706. in marijuana use across the 2012 Washington 100. Chung C, Salottolo K, Tanner A, et al. The im- 116. Fischer B, Russell C, Sabioni P et al. Lower-risk State recreational legalization: is retrospective pact of recreational marijuana commercializa- cannabis use guidelines: a comprehensive up- assessment of use before legalization more ac- tion on traumatic injury. Inj Epidemiol 2019;6: date of evidence and recommendations. Am J curate? J Stud Alcohol Drugs 2018;79:495-502. 3. Public Health 2017;107:e1-12. 85. Darnell AJ, Bitney K. I-502 evaluation and 101. Aydelotte JD, Brown LH, Luftman KM et al. benefit-cost analysis: second required report. Crash fatality rates after recreational marijuana DOI:10.1002/wps.20735 Olympia: Washington State Institute for Public legalization in Washington and Colorado. Am J Policy, 2017. Public Health 2017;107:1329-31. 86. Anderson DM, Hansen B, Rees DI et al. Asso- 102. Sevigny EL. The effects of medical marijuana ciation of marijuana laws with teen marijuana laws on cannabis-involved driving. Accid Anal

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