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Psychiatric effects of ANDREW JOHNS BJP 2001, 178:116-122. Access the most recent version at DOI: 10.1192/bjp.178.2.116

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Psychiatric { report these symptoms. Troisi et al 1998) used urine tests on Italian draftees to identify 133 men who used only cannabis. ANDREW JOHNS All individuals with a pre-existing psychosis or severe had been excluded. An adjustment disorder with depressed mood was found in 16%, major in 14%, and dysthymia in 10.5%. The severity of these symptoms was dose-related. No acute psychotic symptoms were reported. Reilly et al 1998) describe the adverse effects found Background Cannabis is commonly UNTOWARD MENTAL among 268 cannabis users who had taken regarded as aninnocuous drug and the EFFECTSOF CANNABIS the drug for at least 10 years, and who con- tinued to smoke about two refers a day. prevalence of lifetime and regular use has The untoward mental effects of cannabis The most common adverse effects were increasedin mostdeveloped countries. may be classified: feelings of anxiety, paranoia or depression However, accumulative evidence 21%), tiredness and low a)Psychological responses such as panic, highlights the risks of dependence and anxiety, depression or psychosis. 21%). other adverse effects, particularly among These effects may be described as Among individuals making serious attempts at suicide, 16.2% met criteria for people with pre-existing psychiatric `toxic' in that they generally relate to excess consumption of the drug. cannabis misuse/dependence compared disorders. with 1.9% of controls ± much of the highly b)Effects of cannabis on pre-existing significant association was thought to be Aims Tore-evaluatethe adverse effects mental illness and cannabis as a risk- due to independent variables including co- factor for mental illness. of cannabisinthecannabis in the generalpopulationgeneral population and morbidity, but it is suggested that cannabis among vulnerable individuals, including c)Dependency or withdrawal effects. misuse makes a direct contribution to the those with serious psychiatric disorders. The effects of cannabis on cognition are risk of serious self-harm, either directly or separately reviewed by Ashton 2001, this by aggravation of other mental disorders Method A wide-ranging review of the issue). Beautrais et al, 1999). topics related to these issues. PSYCHOLOGICAL Results and conclusions An Cannabis and psychosis RESPONSES TO CANNABIS appreciable proportion of cannabis users Cannabis use can lead to a range of short- lived symptoms such as depersonalisation, report short-lived adverse effects, There is good evidence that taking cannabis derealisation, a feeling of loss of control, leads to acute adverse mental effects in a including psychotic states following heavy fear of dying, irrational panic and para- high proportion of regular users. Many of consumption, and regular users are at risk noid ideas Thomas, 1993). For example, these effects are dose-related, but adverse Thomas 1996) reported that, among of dependence.People with major mental symptoms may be aggravated by con- cannabis users who responded to his sur- illnesses such as are stitutional factors including youthfulness, vey, 15% identified psychotic symptoms personality attributes and vulnerability to especially vulnerable ininthatcannabis that cannabis such as hearing voices or having un- serious mental illness. generally provokes relapse and aggravates warranted feelings of persecution or risk existing symptoms.Health workers need of harmfrom others. Two small case stu- Cannabis and mood change to recognise, and respond to, the adverse dies have reported prolonged depersonal- The acute response to cannabis generally isation after cessation of cannabis use effects of cannabis on mentalhealth. includes euphoria and feelings of detach- Szymanski, 1981; Keshaven & Lishman, Declaration of interest This review ment and relaxation. Adverse effects are 1986). `Flashbacks' or the subsequent not uncommon: these are generally short- partial re-experience when drug-free of was commissioned and funded by the lived, but may persist or recur with symptoms experienced during intoxication Department of Health, but the findings continued use of the drug. are rarely reported after cannabis use are those of the author alone. From New Zealand, a sample of 1000 Thomas, 1993). people aged 18±25 were asked to complete The casual use of the term `cannabis a self-administered questionnaire on psychosis' in clinical psychiatric practice cannabis use and related problems and in the scientific literature results in Thomas, 1996). Those respondents who diagnostic imprecision and research of admitted using cannabis 38%) were asked uncertain validity. Thornicroft 1990) re- about mental health consequences; of these, views the possible associations between 22% reported panic attacks or anxiety. cannabis use and psychosis and suggests {See editorial, p.98, thisissue. Women were twice as likely as men to that common methodological failings are:

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a) studies fail to adequately separate or- 5120 soldiers using cannabis at least three illness, that is a state resembling the psy- ganic from functional psychotic reactions timesa week, 720 presented with chosis of acute schizophrenia without the to cannabis; b) they have insufficiently dis- cannabis-relatedcannabis-related problems. The and confusion of a toxic psychosis. criminated between psychotic symptoms available was potent, containing 5±10% Tennant & Groesbeck 1972) identified and syndromes of a psychosis; and c) they THC). The authors 115 cases of schizophrenic reaction among have not balanced the weight of evidence identified 19 cases of a panic attack or the 720 regular users of cannabis; however, for and against the category of cannabis short-lived toxic psychosis, which appeared all but three had used cannabis with other psychosis. Although there is good evidence after a single high dose of hashish, and a drugs or . Thacore & Shukla for believing that cannabis use may in further 85 cases of toxic psychosis which 1976) compared 25 individuals with a certaincircumstances contribute to appeared after the consumption of cannabis putative diagnosis of `cannabis psychosis psychotic disorders, the connections are with other drugs. These acute states tended of the paranoid type' with controls diag- complex. to resolve within 3 days. nosed with paranoid schizophrenia. Hall et al 1994) suggest that the funda- From Calcutta, Chopra & Smith 1974) Patients with cannabis psychosis showed mental questions are: is there a cannabis retrospectively identified 200 in-patients more bizarre behaviour, violence, panicky psychosis, and does cannabis precipitate who showed serious psychiatric symptoms affect, more insight and less evidence of an underlying psychosis? In theory, canna- after taking cannabis. The most common thought disorder. They also showed a rapid bis use may precipitate a psychosis in the symptoms in all patients were sudden response to neuroleptics with complete following ways. onset of confusion, often associated with recovery. More robust in methodology is a)Acute use of large doses of the drug hallucinations and emotional lability. the work of Rottanburg et al 1982) in may induce a toxic or organic psychosis Disorientation, depersonalisation and which 20 patients with psychosis and with with symptoms of confusion and hallu- paranoid symptoms were common. Many high urinary were compared cination, which remit on abstinence. patients had taken a large dose of cannabis, with 20 matched cannabis-free controls. which was followed by an intoxicated state Mental state was assessed using the Present b)Cannabis use may lead to an acute functional psychosis, similar to an for which they were subsequently amnesic. State Examination PSE) Wing et al, acute schizophreniform state and Among the 34% of patients without a 1974). The cannabis-positive patients had lacking the organic features of a toxic previous history of psychiatric disorder, more symptoms of hypomania and psychosis. adverse symptoms lasted no more than a agitation, less auditory hallucinations, few days, followed by full recovery. A pre- flattening of affect, incoherent speech and c)Cannabis use may lead to a chronic vious history of schizophrenia or person- hysteria than controls. Clouding of con- psychosis, which persists after absti- ality disorder was associated with longer sciousness was absent in most cannabis nence. duration of adverse symptoms. patients. They also showed marked d)Long-term cannabis use may lead to an From Pakistan, Chaudry et al 1991) improvements in symptoms within a week, organic psychosis which only partially report on effects of , a potent while the controls remained unwell despite remits after abstinence, leaving a beverage made from an infusion of canna- receiving comparable antipsychotic drugs. residual deficit state, sometimes called bis leaves and flowering tops. They identi- The authors conclude that a high intake an , which is fied 15 patients who having taken bhang, of cannabis may be related to a rapidly re- thought to be analogous to the chronic presented with a psychosis with symptoms solving psychosis with marked hypomanic organic brain syndrome seen after prolonged misuse of alcohol. of grandiosity, excitement, hostility, dis- features. However, 16 cannabis-positive orientation, hallucinations and thought psychotic patients left the study pre- e)Cannabis use may be a risk-factor disorder. Mental state was assessed system- maturely, which may bias the findings on for serious mental illness such as atically, using the Brief Psychiatric Rating the 20 who remained. Rapid resolution of schizophrenia. Scale BPRS) Lukoff et al, 1986). The symptoms is also reported by Carney et al control group of 10 patients all used bhang, 1984), who identified nine patients with Cannabis and toxic psychosis but less frequently than the study group. cannabis-related psychotic episodes. Their Apart from single-case reports, the nature This work suggests that cannabis, differing symptomatology was described of cannabis-induced toxic psychosis is especially in high doses, can produce a as `schizophreniform, manic, delusional considered in the following studies, all of toxic psychosis in individuals who have psychosis and confusion'. which are weakened by the lack of urine- no history of severe mental illness. The More recently, Mathers & Ghodse testing to confirm the presence of cannabis main features are mild impairment of con- 1992) carried out a prospective study of and the absence of other drugs of misuse. sciousness, distorted sense of passage of in-patients with psychotic symptoms and Talbott & Teague 1969) described 12 time, dream-like euphoria, progressing to cannabis-positive urine. Blind to the urine soldiers in Vietnam who, after their first fragmented thought processes and halluci- test result, researchers applied the PSE on admitted use of cannabis, showed dis- nations, generally resolving within a week admission and again at 1 and 6 months. orientation, impaired , confusion, of abstinence Lishman, 1998). Concurrently admitted patients with psy- reduced span and disordered chosis but with drug-free urine analysis thinking with labile effect and hallu- were controls. At 1 week the two groups cinations. These symptoms resolved within Cannabis and acute functional differed significantly on only five PSE a week. Tennant & Groesbeck 1972) psychosis items: changed perception, thought inser- describe psychoses among 36 000 US A number of studies suggest that heavy tion, non-verbal auditory hallucinations, servicemen stationed in Germany. Of the cannabis use can lead to an acute functional delusions of control, and delusions of

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grandiose ability; this symptom cluster at 1 supporting evidence largely comprises un- episode of psychosis and found 1-year pre- week was thought to be consistent with controlled studies of long-term cannabis valence rates of 19.5% for drug misuse, acute cannabis intoxication. These differ- users in various cultures Hall et al, 11.7% for alcohol misuse, and cannabis ences were minor at 1 month and absent 1994). It is probable that amotivational was the most commonly misused substance. at 6 months. Chronic cannabis-induced syndrome represents nothing more than Given these findings, it is necessary to psychosis was not found. Caucasian ongoing intoxication in frequent users of review the possible role of cannabis as a patients were more likely to be depressed the drug Negrete et al, 1986) and the valid- risk factor for functional illness and for with depersonalisation and derealisation, ity of this diagnosis remains uncertain Hall the aggravation of symptoms. while African±CaribbeansAfrican±Caribbeans showed more et al, 1994). culturally influenced delusions. However, these findings could not be replicated by Effects of cannabis on severe mental illness Cannabis as risk-factor for serious McGuire et al 1994) who also used the Given that high doses of cannabis can cause mentall illness PSE to assess the psychopathology of 23 a toxic psychosis, then it may be supposed patients with psychosis who were cannabis- Comorbidity rates it will aggravate the symptoms of schizo- positive on urinary screening, and 46 Cannabis use is associated with high rates phrenia. However, clinical experience sug- matched drug-free controls. Cases and of comorbidity for other psychiatric diag- gests that some patients say that they take controls were indistinguishable in terms of noses. The Epidemiologic Catchment Area cannabis as a form of `self-medication'. psychopathology, DSM±III diagnoses ECA) survey Regier et al, 1990) of For example, Dixon et al 1990) inter- American Psychiatric Association, 1980), 20 000 subjects in community and in- viewed 83 patients with schizophrenia or onset of recent illness, the proportion of stitutional settings showed that 50.1% of schizophreniform psychoses who reported firstfirst admissions, ethnicity and socio- individualswith cannabis dependence/ that cannabis reduced anxiety and depres- economic class, differing only in their misusealso met DSM±III criteria for one sion, led to increased suspiciousness and histories of substance use. other non-drug or alcohol . had varied effects on drive and hallucina- Having compared groups of drug- Among 133 Italian draftees, Troisi et al tions. Arndt et al 1992) investigated a misusing patients with psychosis of varying 1998) found that the prevalence of co- cohort of 131 patients with schizophrenia duration, Tsuang et al 1982) concluded morbidity was significantly related to the and found that previous use of cannabis that the shorter-duration disorders were pattern of cannabis use: 69% of subjects had no impact on current symptoms. drug-induced toxic psychoses, and the with DSM±III±R cannabis dependence, Peralta & Cuesta 1992) reported that longer-lasting disorders represented the 41% of those with cannabis abuse and cannabis had no significant effect on expression of functional psychiatric illness 24% of occasional users reported at least positive symptoms of schizophrenia, but it in vulnerable individuals. If corroborated, one DSM±III±R Axis 1 psychiatric diag- did attenuate negative symptoms. this suggests that the `functional psychosis' nosis. Most common were adjustment dis- On the other hand, there are a few con- related to cannabis use is best explained as order with depressed mood nˆ21), major trolled studies that have tended to demon- a precipitated episode of an underlying depression nˆ19) and dysthymia nˆ14). strate that cannabis aggravates the severity functional illness. The severity of symptoms also increased of positive symptoms. Negrete et al 1986) with degree of cannabis use. Psychotic described the history of confirmed cannabis symptoms were not found, but it should use in 137 patients with schizophrenia in Cannabis and chronic psychosis be noted all individuals with psychotic ill- treatment. Subjects who were using canna- Ghodse 1986) has suggested that regular ness or severe personality disorder were bis over the 6-month observation period heavy users of cannabis may suffer repeated not drafted. presented with significantly greater short episodes of psychosis and effectively There are high rates of drug misuse delusions and hallucinations, and made `maintain' themselves in a chronic psy- among people with mental illness. The more use of psychiatric services. Similarly, chotic state. This is a possibility, but Hall ECA study Regier et al, 1990) showed that Cleghorn et al 1991) found that drug-users et al 1994) note that it is difficult to distin- the risk of meeting criteria for a substance with schizophrenia, among whom cannabis guish between a chronic cannabis psychosis misuse disorder was 4.6 times higher in was the most heavily used drug, had a high- and the co-occurrence of an illness such as those suffering from schizophrenia than in er prevalence of hallucinations, delusions schizophrenia with continued cannabis the general population. Schizophrenia was and other positive symptoms. This finding use. There is however, no robust evidence associated with a six-fold increase in risk was replicated by Baigent et al 1995), that heavy cannabis use may lead to a psy- of developing a drug use disorder, and can- who reported that among 53 in-patients chotic illness which persists after abstinence nabiswas the most commonly misused with a dual diagnosis of substance misuse Thomas, 1993). drug.Menezes et al 1996) examined the and schizophrenia, cannabis was the only prevalence of substance misuse problems drug that worsened positive symptoms. among 171 patients with psychotic illness Data from the ECA survey Swanson Cannabis and amotivational who had any contact with mental health et al, 1990) also casts some light on the syndrome treatment services in a south London area. possible effects of It has been suggested that heavy cannabis Alcohol problems were more prevalent, and violence. Subjects were asked about use could lead to an `amotivational syn- but current use of one or more drugs was episodes of violence in the previous year drome' described as personality deterio- found in 35 subjects 20%); all but two said i.e. hitting a partner, bruising a child, rationwith loss of energy and drive to they used cannabis. Cantwell et al 1999) fighting, using a weapon in a fight while work Tennant & Groesbeck, 1972). The studied 168 subjects presenting with a first drinking). Of the 191 respondents with

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cannabis abuse or dependence, 19.25% of alternative explanations. There is a large cannabis-withdrawal syndrome has now risk ratio 9.4) had been violent compared temporal gap between self-reported canna- been unequivocally demonstrated and in- with 12.69% risk ratio 6.2) of those with bis use on conscription and the develop- cludes restlessness, anxiety, dysphoria, schizophrenia or schizophreniform dis- ment of schizophrenia over 15 years, and irritability, insomnia, anorexia, muscle order and 24.57% risk ratio 11.9) of no data as to whether the cannabis use con- tremor, increased reflexes and autonomic those with or dependence. tinued during this time. Drugs other than effects including changes in heart rate, Here, the risk is expressed relative to the cannabis could have been taken at any time blood pressure, sweating and diarrhoea. 2.05% who were violent among those of after conscription. The syndrome may appear in about 10 the sample population who showed no It should also be noted that as only 49 of hours, and peaks at about 48 hours psychiatric disorder. However, this does the 274 conscripts with schizophrenia had Mendelson et al, 1984). not amount to a causal correlation between ever tried cannabis, then this drug may only cannabis co-morbidity and violence, given be relevant to a minority of cases. Further- The validity of cannabis the possible role of intervening variables more, Jablensky et al 1992) demonstrate a dependence such as individual and social factors. striking uniformity in the incidence of The Diagnostic and Statistical Manual of That also has an schizophrenia in cultures with very different Mental Disorders DSM±IV; American adverse effect on the course of schizo- rates of cannabis consumption. Psychiatric Association, 1994) presents phrenia was noted by Negrete et al 1986) The possibility of a genetic explanation criteria for the diagnosis of psychoactive and confirmed in a prospective study by for the association between cannabis use , based largely on Linszman et al 1994). A cohort of newly and schizophrenia was raised by McGuire the concept of the dependence syndrome admitted patients with schizophrenia were et al 1994). In this study, 23 patients with Edwards et al, 1981). The key features of assessed monthly for a year, using the psychosis and with cannabis in their urine DSM±IV substance dependence are cogni- BPRS and self-reports of cannabis use. The were gender-matched with 46 drug-free tive, behavioural and physiological symp- cannabis-using group nˆ24) experienced controls with psychosis, and the lifetime toms, indicating that the individual significantly more and earlier psychotic risk of psychiatric disorder among all the continues to use the substance despite signi- relapses and this effect was dose-related. first-degree relatives was ascertained. The ficant substance-related problems. The As Hall et al 1994) remark, these find- cannabis-positive subjects had a signifi- criteria include tolerance, a withdrawal ings are a slender basis on which to draw cantly greater 7.1%) familial risk of syndrome, difficulty in controlling con- conclusions about the effect of cannabis schizophrenia than controls 0.7%), sumption and a pattern of use which leads on schizophrenic symptoms. Until further suggesting that the development or re- to a reduction in other important activities. prospective studies have been carried out, currence of acute psychosis in the context In an empirical study, Morgenstern et al it would be prudent to regard cannabis as of cannabis use may be associated with a 1994) found the DSM concept of cannabis a vulnerability factor in relation to major genetic predisposition to schizophrenia. dependence as least as valid as those for mental illness and to caution at-risk dependence on alcohol, opiates, individuals against using the drug. and . CANNABISDEPENDENCE

Cannabis as risk factor for mental illness Evidence for cannabis dependence Prevalence and course of cannabis There is no evidence that cannabis is a cau- It had been believed that cannabis use did dependence sal factor in schizophrenia and it is more not lead to tolerance and that there was From ECA data, Anthony & Helzer 1991) relevant to consider whether the misuse of no withdrawal syndrome. However, since showed that men had a higher prevalence the drug constitutes a risk factor for this the mid-1970s, these views have been 7.7%) of cannabis abuse or dependence illness. Supporting evidence is found in a challenged by many experimental and than women 4.8%). This was largely due prospective study by Andreasson et al observational studies. For example, Jones to the greater exposure to illicit drugs of 1987) of 45 570 Swedish conscripts, of & Benowitz 1976) administered oral men, since the prevalence of a diagnosis of whom 9.4% had used cannabis and 1.7% THC in doses of 70±210 mg/day to subjects abuse/dependence among those who had were `high consumers' having used more for 30 days and noted a progressive loss of used cannabis more than five times was than 50 times. Fifteen-year follow-up data the subjective `high'. This finding was repli- the same in men and women 21% and were drawn from national registers of cated by Georgotas & Zeidenberg 1979), 19%, respectively). Extrapolating from deaths and psychiatric cases. Compared who gave an average daily dose of 210 mg these data, Hall et al 1994) suggest that with non-users, the relative risk of schizo- THC to volunteers for a 4-week period ± about 17% of those who used cannabis phrenia was 2.4 in the group that reported the subjects then ``found that the more than five times would meet DSM±III use of cannabis at least once, rising to 6.0 was much weaker''. Withdrawal signs were criteria for dependence, and that for those among heavy users. Nearly half 430/730) also found: during the first week of absti- who have ever used there is approximately of these high consumers had a psychiatric nence the subjects ``became very irritable, a 1/10 risk. diagnosis other than psychosis on conscrip- uncooperative, resistant and at times From a New Zealand birth cohort of tion; controlling for this reduced the rela- hostile''; they also became hungry and 1265 children, Fergusson & Horwood tive risk to 2.9. The authors suggest that experienced insomnia. These effects waned 2000) found that by the age of 21, nearly cannabis consumption is a `life-event stres- over 3 weeks. Cessation of smoked cannabis 70% had used cannabis and over 9% met sor' for individuals vulnerable to schizo- has also been shown to lead to withdrawal DSM±IV criteria for cannabis dependence. phrenia. Hall et al 1994) offer a number symptoms Haney et al, 1999). The Key predictors were male gender, ethnic

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minoritystatus and measures of adoles- youthfulness, personality and misuse of contrast with 8% who had used only can- cent risk-takingrisk-taking behaviours, including other drugs, may act as vulnerability factors nabis. Clinical observation suggests that cigarette smoking, conduct problems and to the adverse mental effects of cannabis. cannabis users who also misuse other drugs a delinquent peer group. Mental illness as a vulnerability factor has or alcohol seem to experience more severe Wiesbeck et al 1996) set out to deter- been reviewed in the previous section. mental health problems than those who minethe prevalence of the cannabis- solely take cannabis, but there do not withdrawal syndrome in people who had Adolescence appear to be any substantial published used the drug but who were not in treat- studies on this issue. Polydrug use is a There are a number of reasons why adoles- ment. In a cohort of 5611 individuals, recognised concern in psychiatric popula- cence may be regarded as a time of vulner- 31% had taken the drug on more than 21 tions: for example, Baigent et al 1995) ability for the adverse mental effects of occasions in a year. Among these more found that 20% of their dual-diagnosis cannabis. First, adolescents may experience frequent users, 16% met criteria for a #patients misused more than one substance. emotional problems that cue cannabis use, cannabis-withdrawal syndrome ± i.e. at and their relative youth may lead to an least any one of the following: feeling increased risk of adverse mental states on Personality nervous or irritable, insomnia, tremor, using the drug. Second, regular use of Given the heterogeneity of the population sweats, nausea, gastrointestinal disturbance cannabis may interfere with learning and of cannabis users, it is not surprising that or appetite change. These individuals had personal development. Last, early initiation no single personality type or disorder is used the drug almost daily for an average of cannabis use may predict an increased particular to users of that drug or, indeed, of 70 months and even when use of alcohol risk of escalation in risk and progression to users of any illicit drug Allen & Frances, and other drugs was considered, cannabis to other drugs. 1986). However, it is a matter of clinical use was still significantly related to a self- With regard to the possible impact of observation that the use of cannabis by report of a history of cannabis withdrawal. emotional problems, Newcombe & Bentler some individuals seems to be predisposed Thomas 1996) found that 35% of 1988) found a strong relationship between by traits such as social anxiety, anxiety or cannabis users said that they could not stop adolescent drug use and the experience of dysphoria. Such posited use as a form of when they wanted to, 24% continued to emotional distress, depression and lack of self-medication to relieve unwanted affects use despite problems attributed to the drug a sense of purpose in life. As to the prospect or feelings was not corroborated in a study and 13% felt that they could not control of adverse mental states on using high doses of cannabis-dependent individuals Greene their consumption. Restlessness or irrit- of cannabis, this review has demonstrated et al, 1993). There is good evidence for ability if they could not use cannabis was dose-related effects in adults and the the comorbidity of drug misuse and some reported by 20% of those surveyed. younger user is not likely to be at any lesser personality disorders. For example, Regier Interestingly, dependent users were no more risk. Crowley et al 1998) found that for et al 1990) report that some form of likely to report panic or psychotic episodes adolescents with conduct problems, canna- was identified in 83.6% than those classed as non-dependent. With bis use was not benign in that misuse was of individuals with antisocial personality regard to untoward social consequences, associated with high rates of dependence disorder ASPD), with an odds ratio of 14% of cannabis users agreed that the con- and withdrawal. 29.6. It should be appreciated that this very sumption of the drug had caused them to The possible effects of cannabis con- high rate arises because substance abuse is neglect activities previously considered sumption on the educational performance one of the major diagnostic criteria for important or enjoyable. These findings of adolescents are not easy to demonstrate ASPD; only 16% of individuals with ASPD Thomas, 1996) have to be qualified by the in population studies Hall et al, 1994). did not have a history of substance abuse. low overall response rate of 35%, the use Newcombe & Bentler 1988), having con- The same study showed that the lifetime of unvalidated criteria for cannabis trolled for the higher nonconformity and prevalence of ASPD in cannabis abuse or dependence and by the lack of data on the lower academic potential among dependence was 14.7% with an odds ratio misuse of alcohol or other drugs among the adolescent drug users, found only a modest of 8.3. The interaction between ASPD and sample. negative link between drug use and college cannabis use is too complex to explore at Swift et al 1998) interviewed a sample involvement. Schwartz et al 1989) found length in this review, but it is probable that from New South Wales of 243 long-term short-term memory impairment in 10 each disorder exacerbates the adverse cannabis users who were smoking 3±4 cannabis-dependent adolescents compared effects of the other. See Dolan & Coid times a week. A lifetime prevalence of with matched controls. Test results tended 1993) for a discussion of factors determin- 57% was found for both DSM±III±R and to improve over 6 weeks, which suggested ing outcome in ASPD. ICD±10 World Health Organization, that the deficits observed were due to past 1992) dependence, but only a quarter per- cannabis use. ceived that they had a cannabis problem. Implications for mental health care How should mental health services respond Polydrug use to these findings? The key priorities are: a) VULNERABILITY A substantial number of young people in risk-management and care-planning have TOADVERSETO ADVERSE EFFECTS the community use a range of drugs which to be informed by a thorough substance- OF CANNABIS includes cannabis. Ramsay & Percy misuse assessment Johns, 1997); b) com- 1996) found that 4% of a group of 16- munity and in-patient psychiatric services It has previously been emphasised that to 29-year-olds admitted using cannabis should develop policies on substance use constitutional factors such as relative and other drugs in the past month, by which balance the treatment needs of

120 PSYCHIATRIC EFFECTS OF CANNABIS

individual patients with duties of care to other patients and to the general public; CLINICAL IMPLICATIONS and c) research is needed into treatment in- terventions for patients with mental illness & Among those who have ever taken cannabis,1/10 are at risk of dependence. and substance misuse problems. & Heavy cannabis misuse leads to the risk of psychotic episodes, and aggravates the REFERENCES symptoms andcourse of schizophrenia.

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