Psychology of Addictive Behaviors Types of Cannabis and Tobacco/Nicotine Co-Use and Associated Outcomes in Young Adulthood Joan S

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Psychology of Addictive Behaviors Types of Cannabis and Tobacco/Nicotine Co-Use and Associated Outcomes in Young Adulthood Joan S. Tucker, Eric R. Pedersen, Rachana Seelam, Michael S. Dunbar, Regina A. Shih, and Elizabeth J. D’Amico Online First Publication, April 15, 2019. http://dx.doi.org/10.1037/adb0000464

CITATION Tucker, J. S., Pedersen, E. R., Seelam, R., Dunbar, M. S., Shih, R. A., & D’Amico, E. J. (2019, April 15). Types of Cannabis and Tobacco/Nicotine Co-Use and Associated Outcomes in Young Adulthood. Psychology of Addictive Behaviors. Advance online publication. http://dx.doi.org/10.1037/adb0000464 Psychology of Addictive Behaviors

Types of Cannabis and Tobacco/Nicotine Co-Use and Associated Outcomes in Young Adulthood

Joan S. Tucker, Eric R. Pedersen, Michael S. Dunbar and Rachana Seelam RAND Corporation, Pittsburgh, Pennsylvania RAND Corporation, Santa Monica, California

Regina A. Shih Elizabeth J. D’Amico RAND Corporation, Arlington, Virginia RAND Corporation, Santa Monica, California

Cannabis and tobacco/nicotine use are highly comorbid. Given expanding access to cannabis through legalization for recreational use, it is important to understand how patterns of cannabis and tobacco/ nicotine co-use are associated with young adult outcomes. A predominantly California-based sample of 2,429 young adults (mean age ϭ 20.7) completed an online survey. Based on past-year reports of cannabis and tobacco/nicotine use, we defined 5 mutually exclusive groups: (a) single-product use; (b) concurrent use only (using both products, but only on separate occasions); (c) sequential use only (using both products on the same occasion, one right after the other, but not mixing them together); (d) coadministration only (using both products on the same occasion by mixing them in the same delivery device); and (e) both sequential use and coadministration. We examined group differences in use patterns, dependence, consequences of use, and psychosocial functioning. Fifty percent of respondents reported cannabis use, 43% tobacco/nicotine use, and 37% co-use of both substances. The most prevalent method of co-use involved smoking combustible products. Overall, individuals who co-used both substances on the same occasion in some way reported heavier use and greater problematic behaviors than those who did not. Sequential use (especially among those that also engaged in coadministration) was typically associated with worse physical and mental functioning overall compared to using each substance separately. Findings illuminate both prevalence and risks associated with co-use of cannabis and tobacco/nicotine products and can inform policies for states considering regulation of cannabis and tobacco/nicotine products.

Keywords: marijuana, cannabis, tobacco, nicotine, co-use

In recent years, both cannabis and tobacco/nicotine products electronic nicotine delivery systems (ENDS; Center for Public have become much more widely available to young adults. Stores Health Systems Science, 2016). In addition, there has been a that sell tobacco/nicotine products are ubiquitous. It is estimated proliferation of both cannabis dispensaries and specialty vape that 375,000 U.S. retailers sell conventional tobacco products (e.g., shops (i.e., stores that sell only ENDS, but not other tobacco combustible cigarettes), with 300,000 of these retailers also selling products) in states that have legalized cannabis for recreational sale and possession. For example, specialty vape shops in the United States listed on yelp.com increased from slightly less than

This document is copyrighted by the American Psychological Association or one of its allied publishers. 5,000 in 2002 to almost 10,000 in 2012 (Groskopf, 2016), and

This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. researchers have found that the number of vape shops near college Joan S. Tucker, Eric R. Pedersen, and Rachana Seelam, RAND Corpo- campuses nearly tripled over a 2-year period from 2013 to 2015 ration, Santa Monica, California; Michael S. Dunbar, RAND Corporation, (Dai & Hao, 2017). Given this increasing availability, it is perhaps Pittsburgh, Pennsylvania; Regina A. Shih, RAND Corporation, Arlington, Vir- ginia; Elizabeth J. D’Amico, RAND Corporation, Santa Monica, California. not surprising that there has been an overall upward trend in recent This research was supported by funds from Tobacco-Related Disease Re- years in the co-use of cannabis and tobacco/nicotine products search Program of the University of California, Grant 26IR-0011 to Joan S. among adults in the United States (Schauer, Berg, Kegler, Dono- Tucker, as well as grants from the National Institute of Alcohol Abuse and van, & Windle, 2015). Alcoholism (R01AA016577, R01AA020883, R01AA025848) to Elizabeth J. Prior to the proliferation of different types of cannabis and D’Amico. We thank the districts and schools who participated and supported tobacco/nicotine products and methods of use, co-use of these this project. We thank Kirsten Becker and Jennifer Parker for overseeing the products was generally limited to combustible methods. This could data collection. Correspondence concerning this article should be addressed to Joan S. include smoking each type of product separately or after mixing Tucker, RAND Corporation, 1776 Main Street, Santa Monica, CA 90407. them in some way. Studies indicate that use of one of these drugs E-mail: [email protected] increases the likelihood of using the other. For example, combus-

1 2 TUCKER ET AL.

tible tobacco use has been shown to lead to subsequent initiation of of cannabis dependence (Ream, Benoit, Johnson, & Dunlap, and increases in cannabis use (Agrawal, Budney, & Lynskey, 2008). In addition, coadministration, or mixing the products to- 2012; Agrawal, Lynskey, Bucholz, Madden, & Heath, 2007; Lai, gether, can significantly increase the amount of THC inhaled per Lai, Page, & McCoy, 2000), and young adults who initiate can- gram of cannabis (Rabin & George, 2015). Further, individuals nabis use have been found to subsequently report more combus- who use both cannabis and tobacco/nicotine are at elevated risk of tible tobacco use (Agrawal et al., 2012; Agrawal, Madden, Bu- poorer psychosocial functioning such as worse mental health, cholz, Heath, & Lynskey, 2008; Behrendt, Wittchen, Höfler, Lieb, lower life satisfaction, more legal problems, and poor academic & Beesdo, 2009; Timberlake et al., 2007; Tullis, Dupont, Frost- achievement in college (Georgiades & Boyle, 2007; Hernández- Pineda, & Gold, 2003). Further, studies of young people have Serrano, Gras, & Font-Mayolas, 2018; Moore & Budney, 2001; found that cannabis use can impede their efforts to quit cigarette Suris, Akre, Berchtold, Jeannin, & Michaud, 2007). However, it is smoking (Amos, Wiltshire, Bostock, Haw, & McNeill, 2004; important to better understand whether certain types of co-use Ramo, Delucchi, Hall, Liu, & Prochaska, 2013; Tullis et al., 2003). (e.g., sequential co-use, coadministration) may elevate risk for In recent years, much attention has focused on the dramatic rise in poorer young adult outcomes. the popularity of ENDS products (U.S. Department of Health & Human Services, 2016). ENDS are typically marketed as being used The Present Study to vape e-liquids (which often contain nicotine) but can also be used This study examined different types of co-use as a first step in to consume cannabis (Morean, Kong, Camenga, Cavallo, & understanding more detailed patterns of cannabis and tobacco/ Krishnan-Sarin, 2015; Prieur, 2018). Multiple studies indicate that nicotine use among young adults, an age group that has the highest over half of the people that report using ENDS also report using rates of both cannabis and tobacco/nicotine use (Azofeifa, 2016; cannabis (Berg et al., 2015; Saddleson et al., 2015; U.S. Department Centers for Disease Control & Prevention, 2017; Hasin et al., of Health & Human Services, 2016). In a large nationally represen- 2015, 2016; Schauer et al., 2015; Substance Abuse and Mental tative sample of 18- to 24-year-olds, those who used ENDS in the past Health Services Administration, 2017), as well as co-use of these 30 days were three times more likely to also report use of cannabis products (Centers for Disease Control & Prevention, 2017; during that same period compared to young adults who did not use Schauer et al., 2015). We surveyed a diverse and predominantly ENDS (Cohn et al., 2015). Further, available studies show that greater California sample of 2,429 young adults in 2017–2018 about their use of cannabis is related to greater use of ENDS to vape cannabis use of cannabis and tobacco/nicotine products in the past year. We (Cranford, Bohnert, Perron, Bourque, & Ilgen, 2016; Frohe et al., first describe the prevalence and most common methods of co-use 2017; Jones, Hill, Pardini, & Meier, 2016). The use of ENDS to vape (i.e., unique combinations of products). We categorized partici- cannabis (with or without nicotine) by young adults is also concerning pants into one of five mutually exclusive groups: (a) single- because the short-term and long-term health consequences are largely product use (cannabis only; tobacco/nicotine only); (b) concurrent unknown (Cranford et al., 2016; Giroud et al., 2015; Ramo, Liu, & use only (using both products at some point, but only on separate Prochaska, 2012). occasions); (c) sequential use only (using both products on the Although a research base on cannabis and tobacco/nicotine same occasion, one right after the other, but not mixing them); (d) co-use is emerging, both in the United States and in other countries coadministration only (using both products by mixing them in the (Schauer, Rosenberry, & Peters, 2017), existing work on cannabis same delivery device); and (e) both sequential use and coadmin- and tobacco/nicotine co-use has been limited in several key re- istration. These co-use groups were then compared on their fre- spects. First, most studies were conducted at a time when these quency and heaviness of use, cannabis use disorder, cigarette and substances were almost exclusively smoked and therefore do not e-cigarette dependence, as well as indicators of psychosocial func- reflect the recent proliferation in product types and methods of use tioning. We hypothesized that young adults who engaged in any (Russell, Rueda, Room, Tyndall, & Fischer, 2018). Understanding type of co-use (concurrent, sequential, or coadministration) would young adults’ preferred methods of combining cannabis and to- report worse functioning compared to those who reported bacco/nicotine products is important because certain methods of cannabis-only or tobacco/nicotine-only use. Little research is co-use (e.g., combustible) may pose greater health risks than others available to help form hypotheses for specific co-use groups; (e.g., vaping). Second, studies have often assessed co-use in terms however, we hypothesized that those who used cannabis and This document is copyrighted by the American Psychological Association or one of its alliedof publishers. whether the individual reported using both products during a tobacco/nicotine products together in some way (i.e., sequential This article is intended solely for the personal use ofspecified the individual user and is not to be disseminated broadly. period such as the past year or past month, ignoring use, coadministration, or both) would report poorer outcomes than whether these products were used together in some way—for those who reported use of both substances but on separate occa- example, using both products on the same occasion, one right after sions only (i.e., concurrent use only). the other, but not mixing them together in the same delivery device (sequential use; e.g., smoking a joint and then smoking a ciga- Method rette), or mixing them in the same delivery device (coadministration; e.g., smoking a spliff that contains tobacco rolled in with Sample and Procedure cannabis). These distinctions have important implications for both the quantity consumed and the health effects of use, although Participants originated from two cohorts of 6th- and 7th-grade research in this area is sparse and with methodological limitations students who were initially recruited in 2008 from 16 middle (Meier & Hatsukami, 2016). For example, one study found that schools in southern California as part of a substance use prevention using products on the same occasion or mixing the products in the program, CHOICE (D’Amico et al., 2012). All students in the two same delivery device are both associated with increased symptoms cohorts who were followed to Wave 10 consented to the study CANNABIS AND TOBACCO/NICOTINE CO-USE 3

(N ϭ 6,509), and all procedures were approved by the institution’s Measures review board. Participants completed Wave 1 (Fall, 2008) through Wave 5 (Spring, 2011) during physical education classes. Past year cannabis and tobacco/nicotine use. Separate items Follow-up rates ranged from 74% to 90% during this time period, asked how often participants used each of eight cannabis products excluding new youth that could have come in at a subsequent or devices in the past year: joint to smoke marijuana; blunt (cigar wave. Adolescents transitioned from the 16 middle schools to over shell) that contains only marijuana (no tobacco); handpipe (bowl) 200 high schools following Wave 5 and were subsequently recon- to smoke marijuana; bong (waterpipe) to smoke marijuana; dabs tacted and reconsented to complete annual web-based surveys, for (wax, shatter, budder, hash oil); edibles (e.g., brownies or candy); which they were compensated. At Wave 6 (Spring 2013–Spring electronic cigarette or e-cigarette to smoke/vaporize marijuana; 2014), 61% of the sample participated in the follow-up survey. At and personal vaporizer filled with hash oil, THC wax, dried buds, the subsequent annual assessments, we retained 80% of the sample or other type of marijuana product. Separate items also asked how from Waves 6 to 7, 91% of the sample from Waves 7 to 8, 89% of often participants had used each of the following seven tobacco/ the sample from Waves 8 to 9, and 90% of the sample from Waves nicotine products or devices in the past year: cigarette, smokeless 9 to 10. Demographics (e.g., gender, race/ethnicity, employment) tobacco, hand pipe, hookah, large cigar/little cigar/cigarillo, and substance use at the prior wave (e.g., alcohol, cigarettes, e-cigarette (not for the purposes of using marijuana), and personal marijuana) did not predict attrition at Wave 10, similar to what we vaporizer filled with nicotine e-liquid or other type of tobacco have found at earlier waves (e.g., D’Amico et al., 2016). product. Items were rated on a scale from 1 (none)to6(more than The present analyses use Wave 10 data, which occurred between 20 times). These items were used to identify participants who had July 2017 and June 2018, which is the first wave we added items used a single type of product (cannabis or tobacco/nicotine) versus assessing different types of co-use. The full sample at Wave 10 both cannabis and tobacco/nicotine products in the past year. consists of 2,429 respondents, with an average age of 20.67 years Past year cannabis and tobacco/nicotine co-use. Participants who (SD ϭ 0.70). The sample is 45.62% male, 20.13% non-Hispanic reported use of both cannabis and tobacco/nicotine rated how often in White, 45.20% Hispanic, 20.75% Asian, 10.13% multiethnic, 2.31% the past year they had “used both of these products/devices, one right Black, and 1.48% other races/ethnicities. The majority were still after the other,” rated on a scale from 1 (none)to6(more than 20 residing in California (93%) and were currently in college or trade times), as an indicator of sequential use. In addition, participants school (80.28%). Within the full Wave 10 sample, 1,222 respondents completed 10 items on how often they had “mixed tobacco and reported past year cannabis use and 1,036 reported past year tobacco/ marijuana together” in different ways (cigarette dipped in hash oil; nicotine use (as defined below). These two groups are the main focus cigarette, joint, blunt, bong, hookah, hand pipe/bowl, or any other of analyses, and their characteristics are presented in Table 1. method that contained both tobacco and marijuana; e-cigarette or personal vaporizer that contained both nicotine e-liquid and marijuana), rated on a scale from 1 (none)to6(more than 20 times), as an indicator of coadministration. We then calculated the percent of Table 1 participants who reported each type of sequential use and each type of Sample Characteristics coadministration. Given the strong correlation between e-cigarette and personal vaporizer use (r ϭ .60 for any use; r ϭ .70 for fre- Past year Past year cannabis use tobacco/nicotine quency), and potential for some participants to not differentiate be- group use group tween these terms for ENDS devices (Coleman, Johnson, Alexander, (n ϭ 1,222) (n ϭ 1,036) & Williams, 2018), we combined reported use of e-cigarettes or Characteristic n/M %/SD n/M %/SD personal vaporizer into a single ENDS category. From this information we created five mutually exclusive groups based on reports of Demographics whether they had engaged in the following types of cannabis and Age 20.65 .69 20.68 .71 Race/ethnicity tobacco/nicotine use in the past year (yes/no): (a) single-product use Hispanic 516 42.23% 444 42.86% (cannabis only; tobacco/nicotine only); (b) concurrent use only (using Non-Hispanic both products, but only on separate occasions); (c) sequential use only White 319 26.10% 261 25.19% (using both products at the same time, but not mixing them); (d)

This document is copyrighted by the American Psychological Association or one of its allied publishers. Asian 209 17.10% 185 17.86% coadministration only (using both products by mixing them in the

This article is intended solely for the personal use of the individual user and is notBlack to be disseminated broadly. 30 2.45% 18 1.74% Multiracial 134 10.97% 115 11.10% same delivery device); and (e) both sequential use and coadministra- Other 14 1.15% 13 1.25% tion. Male 577 47.22% 531 51.25% Frequency of marijuana, cigarette, and e-cigarette use. In college/trade school 984 80.52% 819 79.05% 1 Co-use status Measures of marijuana , cigarette, and e-cigarette use were based No co-use 344 28.15% 182 17.57% on items from Monitoring the Future asking how often they had Concurrent use only 374 30.61% 374 36.10% used or tried each of these products in the past year, rated on a Coadministration use onlya 122 9.98% 99 9.56% none more than 20 times a scale from 1 ( )to6( ). Response options Sequential use only 170 13.91% 173 16.70% were recoded to reflect the midpoint of number of times (e.g., Sequential ϩ Coadministration usea 212 17.35% 208 20.08% a Differences in sample sizes across the cannabis use and tobacco/nicotine 1 Note that survey items on frequency, quantity, and consequences/ use samples for coadministration and sequential use are due to inconsistent problems referred specifically to the use of marijuana, rather than using the reporting (e.g., endorsing a form of co-use, but not the individual cannabis cannabis term. As such, we use the term ‘marijuana’ when referring to and tobacco/nicotine items that comprise the co-use). these items in the Methods, Results, and tables. 4 TUCKER ET AL.

11–20 times ϭ 15.5) using an established approach (National engaged in two marijuana1 problematic behaviors: selling mari- Institute on Alcohol Abuse & Alcoholism, 2003; Osilla et al., juana or driving a car after using marijuana. 2014) to yield a continuous score ranging from 0 to 20 so model Delinquency. Participants were asked about frequency of past estimates could be interpreted as number of times a respondent year engagement in (nonsubstance use) delinquency, such as fight- used each substance/device in the past year. ing, skipping school, getting fired from a job, and getting in trouble Quantity of marijuana, cigarette, and e-cigarette use. For with the police. Items were modified from the RAND Adolescent/ marijuana1, this was assessed by first asking how many times they Young Adult Panel Study (Tucker, Orlando, & Ellickson, 2003) used marijuana on the days they used and, for those who reported at and were rated on a scale from 1 (none)to6(20 or more times) and least one time, asking, “On the days you use marijuana, on a typical summed (␣ϭ.86). use day, how much marijuana flower/bud do you personally consume Mental health. Mental health was assessed with two mea- (don’t include amount you may have shared)?” (Kilmer et al., 2013). sures. The eight-item Patient Health Questionnaire (PHQ-8; Response options ranged from 1 (Ͻ0.25 grams)to10(more than Kroenke et al., 2009) assessed eight symptoms of depression such 5 grams). Response options were recoded to reflect the mid-point as feeling down, depressed, or hopeless and having little interest or number of grams to yield a continuous score ranging from 0.25 to 5.0 pleasure in doing things (␣ϭ.92). The Generalized Anxiety grams. Those who reported using marijuana zero times in the past Disorder 7-item (GAD-7; Spitzer, Kroenke, Williams, & Löwe, year were coded as 0. To encourage accurate responses, we provided 2006) assessed seven symptoms of anxiety such as feeling ner- pictures of 0.5 gram, 1.0 gram, and 3.5 grams (eighth ounce) of vous, anxious, or on edge and not being able to stop or control marijuana flower/bud (Kilmer et al., 2013). We assessed quantity of worrying (␣ϭ.94). Both measures assessed symptoms in the past cigarette and e-cigarette use, respectively, by asking, “On the days two weeks on a scale from 0 (not at all)to3(nearly every day). you smoke cigarettes, how many do you usually smoke” (response Physical health. Physical ailments in the past four weeks options were capped at 20 or more cigarettes per day) and “On the were assessed with four items from the 15-item Patient Health days that you use your e-cigarette, how many times per day do you Questionnaire (PHQ-15; Kroenke, Spitzer, & Williams, 2002) usually use it? Assume that one “time” consists of around 15 puffs or asking how much participants were bothered by stomach pain, lasts around 10 min” (response options were capped at 99 times). headaches, feeling tired or having low energy, and trouble sleeping Those who reported smoking zero cigarettes in the past year or using on a scale from 0 (not bothered at all)to2(bothered a lot). Each e-cigarettes zero times were coded as 0 for these quantity items. item was dichotomized as 0 (not bothered at all)vs.1(bothered a Cannabis use disorder and cigarette/e-cigarette dependence. little/bothered a lot), and the four items were summed to create an We assessed symptoms of cannabis use disorder with the three- overall physical ailment score (␣ϭ.75). Physical health was item Cannabis Use Disorder Identification Test Short-Form assessed with a combination of subjective overall health, ranging (CUDIT-SF; Bonn-Miller, Heinz, Smith, Bruno, & Adamson, from 1 (excellent)to5(poor), and two items from the Patient- 2016). Participants who reported past month marijuana use rated Reported Outcomes Measurement Information System (PROMIS; how often during the past 6 months they found that they were not DeWitt, Stucky, Thissen, Irwin, & Langer, 2011) for ability to able to stop using marijuana/cannabis once they had started; de- physically engage in activities that one enjoys and ability to voted a great deal of their time to getting, using, or recovering participate in sports/activities similar to their peers ranging from 1 from marijuana/cannabis; and had problems with their memory or (with no trouble)to5(not able to do). Items were reverse scored concentration after using marijuana/cannabis. Items were rated on and summed, with higher scores indicating better physical health a scale from 0 (never)to4(daily or almost daily) and then (␣ϭ.80). summed (␣ϭ.70; note that all reported alphas are based on full Social functioning. Lastly, social functioning was assessed wave 10 sample). Among those reporting past month cigarette use, with eight PROMIS peer relationship items (DeWalt et al., 2013) we used latency to first cigarette (“How soon after waking do you rated from 0 (never)to4(always). Items included “I was able to smoke your first cigarette?”) as an indicator of cigarette depen- count on my friends,” “I felt accepted by other people my age,” dence (Baker et al., 2007). Similarly, for past month e-cigarette and “I was good at making friends” (␣ϭ.96). use, we used latency to first e-cigarette (“On days that you use Sociodemographics and race/ethnicity. Variables included your electronic cigarette freely, how soon after waking do you first age, gender, current attendance in college/trade school, and race/ use your electronic cigarette”) as an indicator of e-cigarette de- ethnicity. Participants were classified into one of six racial/ethnic This document is copyrighted by the American Psychological Association or one of its allied publishers. pendence (Foulds et al., 2015). Both items were rated on a 4-point groups: Hispanic and five non-Hispanic groups—White (reference This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. scale, ranging from 1 (within 5 min)to4(after 60 min). group), Black, Asian, Multiracial (more than one race), and Other Marijuana consequences and problems. Negative conse- (e.g., Native American, Native Hawaiian). quences due to marijuana1 use in the past year were assessed with a 10-item measure based on items from the RAND Adolescent/ Analytic Approach Young Adult Panel Study (Ellickson, D’Amico, Collins, & Klein, 2005) and the Marijuana Consequences Questionnaire (Simons, Analyses describing the prevalence of different types of sequen- Dvorak, Merrill, & Read, 2012). Respondents were asked how tial use (see Table 2) and coadministration (see Table 3) within the many times various things had happened to them in the past year full sample, and among those who reported using both cannabis because of using marijuana (sample items: missed school, work, or and tobacco/nicotine in the past year, were primarily descriptive. A other obligations; got into trouble; did something you later felt secondary analysis explored differences by gender and race/eth- sorry for). Each item was rated from 1 (none)to7(20 or more nicity, within the full sample, in any sequential use (yes/no) and times) and summed (␣ϭ.91). Using the same response scale, any coadministration (yes/no). Analysis of covariance tests and participants were also asked how often in the past year they follow-up Tukey post hoc tests were conducted to compare the five CANNABIS AND TOBACCO/NICOTINE CO-USE 5

Table 2 Past Year Sequential Co-Use of Cannabis and Tobacco/Nicotine in Full Sample and Among Past Year Cannabis and Tobacco/Nicotine Co-Use Groups (Combinations With Ն 10% Prevalence Among Co-Use Sample Are Shown)

% among % among full co-use Type of sequential co-use sample sample

Any type of sequential co-use (n ϭ 401) 16.51% 44.41% Cigarette ϩ Joint to smoke marijuana (n ϭ 179) 7.41% 19.93% ENDSa ϩ Joint to smoke marijuana (n ϭ 157) 6.46% 17.39% ENDSa ϩ E-cigarette/vaporizer to use marijuana (n ϭ 157) 6.46% 17.39% Cigarette ϩ Blunt (cigar shell) that contains only marijuana (n ϭ 150) 6.21% 16.76% ENDSa ϩ Bong (waterpipe) to smoke marijuana (n ϭ 148) 6.09% 16.39% Cigarette ϩ Bong (waterpipe) to smoke marijuana (n ϭ 141) 5.84% 15.75% ENDSa ϩ Blunt (cigar shell) that contains only marijuana (n ϭ 135) 5.56% 14.95% ENDSa ϩ Hand pipe (bowl) to smoke marijuana (n ϭ 122) 5.02% 13.51% Cigarette ϩ Hand pipe (bowl) to smoke marijuana (n ϭ 117) 4.84% 13.01% Cigarette ϩ E-cigarette/vaporizer to use marijuana (n ϭ 111) 4.57% 12.29% ENDSa ϩ Dabs (wax, shatter, budder, hash oil; n ϭ 104) 4.28% 11.52% ENDSa ϩ Edible (e.g., brownies or candy; n ϭ 102) 4.20% 11.30% Note. ENDS ϭ electronic nicotine delivery systems. N ϭ 2,429 for full sample and n ϭ 903 for co-use sample. Tobacco/nicotine product is listed first, followed by cannabis product. a Indicates endorsement of the item on using e-cigarettes (not for the purpose of using marijuana) and/or the item on use of personal vaporizer filled with nicotine e-liquid or other type of tobacco/nicotine product.

mutually exclusive groups: single substance use; concurrent use 1,036) reported past year use of any tobacco/nicotine product, and only (no sequential use or coadministration); coadministration 37.18% (n ϭ 903) reported past year use of both cannabis and only (no sequential use); sequential use only (no coadministra- tobacco/nicotine products. Sequential use of cannabis and tobacco/ tion); and those who reported both sequential use and coadminis- nicotine (using both products at the same time, one right after tration. Separate analyses were conducted to compare the another, but not mixing them) was reported by 401 respondents, cannabis-only use group to each co-use group (see Table 4), and to which was 16.51% of the full sample and 44.41% of those who compare the tobacco/nicotine-only use group to each co-use group used both products in the past year. Coadministration of cannabis (see Table 5). These group comparisons controlled for sociodemo- and tobacco/nicotine (using both at the same time by mixing them graphic covariates described above. in the same delivery device) was reported by 342 respondents, which was 14.08% of the full sample and 35.87% of those who Results used both products in the past year. Secondary analyses exploring racial/ethnic differences found an Prevalence and Methods of Cannabis and Tobacco/ overall difference in both sequential use, F(5, 2423) ϭ 3.45, p ϭ Nicotine Co-Use .004, and coadministration, F(5, 2423) ϭ 15.13, p Ͻ .001, within In the full sample (N ϭ 2,429), 50.31% (n ϭ 1,222) of respon- the full sample. Tukey post hoc comparisons found that sequential dents reported past year use of any cannabis product, 42.65% (n ϭ use was more common among non-Hispanic Whites than Hispan-

Table 3 Past Year Coadministration of Cannabis and Tobacco/Nicotine in Full Sample and Among Past Year Cannabis and Tobacco/Nicotine Co-Use Groups

This document is copyrighted by the American Psychological Association or one of its allied publishers. % among

This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. % among full co-use Type of coadministration sample sample

Any type of coadministration (n ϭ 342) 14.08% 35.87% Joint that contains both tobacco and marijuana (n ϭ 243) 10.03% 27.00% Bong that contains both tobacco and marijuana (n ϭ 191) 7.89% 21.27% Blunt that contains both tobacco and marijuana (n ϭ 188) 7.76% 20.89% Cigarette that contains both tobacco and marijuana (n ϭ 104) 4.29% 11.56% Hand pipe or bowl that contains both tobacco and marijuana (n ϭ 92) 3.80% 10.22% ENDS that contains both nicotine e-liquid and marijuana (such as hash oil, THC wax, dried buds; n ϭ 79) 3.25% 8.75% Any other way of using both tobacco and marijuana through the same delivery device (n ϭ 58) 2.40% 6.45% Hookah that contains both tobacco and marijuana (n ϭ 49) 2.02% 5.44% Cigarette dipped in hash oil (n ϭ 48) 1.98% 5.33% Note. ENDS ϭ electronic nicotine delivery systems. N ϭ 2,429 for full sample and n ϭ 903 for co-use sample. 6 TUCKER ET AL.

Table 4 Comparing Cannabis Only Use Group to Concurrent Use, Sequential Use, and Coadministration Use Groups

Group 1: Group 2: Group 3: Group 4: Group 5: Cannabis Concurrent Co-admin. Sequential Sequential ϩ co- Overall use only use only only use only administration ANCOVA Variable M (SE) M (SE) M (SE) M (SE) M (SE) F (df ϭ 8) Group differencesa

Frequency of marijuana use 8.55 (.40) 9.94 (.38) 15.05 (.67) 12.60 (.57) 17.30 (.51) 32.82‡ 1/3, 2/3, 1/4, 2/4, 3/4, 1/5, 2/5, 4/5 Quantity of marijuana use .58 (.05) .53 (.05) .90 (.08) .94 (.07) 1.04 (.06) 17.67‡ 1/3, 2/3, 1/4, 2/4, 1/5, 2/5 CUDb 1.02 (.19) 1.21 (.17) 1.83 (.26) 1.54 (.22) 2.81 (.18) 12.15‡ 1/5, 2/5, 3/5, 4/5 Marijuana consequences 13.11 (.46) 14.12 (.44) 18.30 (.77) 16.64 (.65) 22.29 (.59) 28.32‡ 1/3, 2/3, 1/4, 2/4 1/5, 2/5, 3/5, 4/5 Marijuana selling .04 (.02) .05 (.02) .15 (.03) .16 (.02) .23 (.02) 14.76‡ 1/3, 2/3, 1/4, 2/4 1/5, 2/5 Marijuana-impaired driving .15 (.02) .21 (.02) .47 (.04) .38 (.03) .55 (.03) 21.62‡ 1/3, 2/3, 1/4, 2/4, 1/5, 2/5, 4/5 Delinquency 6.41 (.15) 6.56 (.14) 6.67 (.25) 7.13 (.21) 8.53 (.19) 15.68‡ 1/4, 1/5, 2/5, 3/5, 4/5 Physical ailments 2.09 (.07) 1.92 (.07) 2.21 (.12) 2.13 (.11) 2.40 (.10) 6.94‡ 2/5 Physical health 12.21 (.13) 12.43 (.12) 12.29 (.21) 11.68 (.18) 11.76 (.16) 6.34‡ 2/4, 2/5 Social functioning 42.66 (.41) 43.18 (.39) 43.99 (.69) 42.41 (.58) 43.17 (.52) 3.97‡ — Anxiety 5.73 (.29) 4.74 (.28) 5.31 (.50) 5.88 (.42) 6.67 (.38) 4.44‡ 2/5 Depression 5.71 (.31) 5.42 (.29) 5.83 (.51) 6.90 (.43) 7.57 (.39) 5.79‡ 1/5, 2/4, 2/5 n 344 374 122 170 212 Note. CUD ϭ cannabis use disorder; ANCOVA ϭ analysis of covariance. Adjusted means and SEs after controlling for age, gender, race/ethnicity, and college status are shown. a Group differences significant at p Ͻ .05 from pairwise comparisons. b Past month marijuana use only (n ϭ 738). ‡ p Ͻ .001.

ics (21.88% vs. 14.12%, p Ͻ .05). Coadministration was more 11.73%; t ϭ 6.84, p Ͻ .0001) and coadministration (18.68% vs. likely among non-Hispanic Whites (24.74%) than Hispanics 10.22%; t ϭ 5.89, p Ͻ .0001). (9.93%), Asians (10.71%), and those in the Other group (5.56%), As shown in Table 2, the most prevalent forms of sequential use, and more prevalent in the Multiethnic group than among Hispanics or using one product right after the other, were cigarette and joint (18.29% vs. 9.93%) (ps Ͻ .05). In addition, males were more (7.41% of full sample), ENDS and joint (6.46%), ENDS and likely than females to engage in both sequential use (22.20% vs. e-cigarette/vaporizer for marijuana (6.46%), cigarette and blunt

Table 5 Comparing Tobacco/Nicotine Only Use Group to Concurrent Use, Sequential Use, and Coadministration Use Groups

Group 1: Group 2: Group 3: Group 4: Group 5: Tobacco Concurrent Co-admin. Sequential Sequential ϩ co- use only use only only use only administration Overall ANCOVA, Variable M (SE) M (SE) M (SE) M (SE) M (SE) F(df ϭ 8) Group differencesa

Frequency of cigarette use 3.58 (.51) 3.74 (.36) 6.97 (.70) 5.77 (.52) 11.01 (.48) 27.36‡ 1/3, 2/3, 1/4, 2/4, 1/5, 2/5, 3/5, 4/5 ‡

This document is copyrighted by the American Psychological Association or one of its alliedFrequency publishers. of e-cigarette use 2.66 (.53) 3.36 (.37) 5.33 (.72) 5.76 (.54) 9.51 (.49) 23.67 1/3, 1/4, 2/4, 1/5, 2/5,

This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. 3/5, 4/5 Quantity of cigarette use .50 (.17) .39 (.12) 1.02 (.23) .96 (.17) 1.71 (.16) 9.00‡ 2/4, 1/5, 2/5, 4/5 Quantity of e-cigarette use 1.66 (.91) 1.97 (.65) 3.20 (1.27) 5.86 (.94) 7.24 (.86) 5.58‡ 1/4, 2/4, 1/5, 2/5 — ءTime to first cigaretteb 3.79 (.12) 3.62 (.09) 3.57 (.14) 3.47 (.10) 3.69 (.07) 2.14 — ءTime to first e-cigarettec 3.47 (.12) 3.39 (.07) 3.31 (.13) 3.22 (.09) 3.31 (.08) 1.98 Delinquency 6.31 (.22) 6.59 (.15) 6.70 (.30) 7.22 (.22) 8.58 (.20) 12.65‡ 1/4, 1/5, 2/5, 3/5, 4/5 Physical ailments 2.05 (.10) 1.89 (.07) 2.15 (.14) 2.14 (.10) 2.40 (.10) 8.79‡ 2/5 Physical health 12.54 (.17) 12.43 (.12) 12.30 (.24) 11.70 (.18) 11.76 (.16) 6.61‡ 1/4, 2/4, 1/5, 2/5 Social functioning 42.67 (.56) 43.22 (.44) 43.87 (.76) 42.49 (.57) 43.07 (.53) 3.70‡ — Anxiety 6.00 (.41) 4.69 (.29) 5.19 (.56) 5.77 (.42) 6.66 (.38) 4.80‡ 2/5 Depression 6.16 (.43) 5.41 (.30) 5.95 (.58) 6.77 (.44) 7.58 (.40) 5.74‡ 2/5 n 182 374 99 173 208 Note. ANCOVA ϭ analysis of covariance. Adjusted means and SEs after controlling for age, gender, race/ethnicity, and college status are shown. a Group differences significant at p Ͻ .05 from pairwise comparisons. b Past month cigarette use only (n ϭ 375). c Past month e-cigarette use only (n ϭ 1,015). .p Ͻ .05 ء .p Ͻ .001 ‡ CANNABIS AND TOBACCO/NICOTINE CO-USE 7

(6.21%), ENDS and bong (6.09%), cigarette and bong (5.84%), cannabis-only group and 10% in the concurrent-only group. ENDS and blunt (5.56%), and ENDS and hand pipe (5.02%). All Lastly, for driving after marijuana use, the three co-use groups that other combinations were mentioned by less than 5% of the full used both products on the same occasion were more likely to drive sample. Table 3 contains the 10 forms of coadministration listed in after using marijuana compared to the cannabis-only group and the order of prevalence. The most common forms of coadministration, concurrent-only group. The sequential ϩ coadministration group or mixing of products, were joints (10.03% of the total sample), was also more likely to drive after using marijuana than the bongs (7.89%), and blunts (7.76%) that contained both marijuana sequential-only group. Compared to 15% of the cannabis-only use and tobacco. All other forms of coadministration were mentioned group, 47% of the coadministration-only group and 55% of the by less than 5% of the full sample. sequential ϩ coadministration group reported driving after use. Delinquency, physical health, mental health, and social Comparing Cannabis-Only Group to the Four functioning. We found overall group differences on delinquency, Co-Use Groups physical ailments, physical health, anxiety, and depression. For delinquency, those in the sequential ϩ coadministration group reported Table 4 contains means and standard errors for each outcome by greater past year delinquency compared to all other groups. In addi- subgroup, as well as the overall analysis of covariance test statistic tion, the sequential-only group reported greater delinquency than the and significant findings between subgroups. cannabis-only group. Regarding physical ailments and health, the Marijuana use and cannabis use disorder. As hypothesized, sample overall reported good physical health; however, the sequen- we found overall group differences on marijuana use and CUDIT-SF tial ϩ coadministration group reported more physical ailments and score based on the use group. The three co-use groups that used poorer health than the concurrent-only group and the sequential-only cannabis and tobacco/nicotine products on the same occasion in some group reported poorer health than the concurrent-only group. For way (coadministration, sequential, or both) reported more days of anxiety, those in the sequential ϩ coadministration group reported marijuana use than the cannabis-only group; however, there was not greater anxiety symptoms than the concurrent-only group. For depres- a significant difference in heaviness of use between the group that had sion, those in the sequential ϩ coadministration group reported used both products in the past year, but never on the same occasion greater depression symptoms than the cannabis-only and concurrent- (concurrent only), and the cannabis-only group. Further, the two only groups, and the sequential-only group reported greater depres- groups that reported coadministration of products reported more fre- sion symptoms than the concurrent-only group. Means across the quent marijuana use than the sequential-only and concurrent-only groups were generally mild to moderate, as scores of 10 on the groups, and the sequential-only group reported more frequent mari- GAD-7 and the PHQ-8 indicate positive screens for anxiety and juana use than the concurrent-only group. depression, respectively. There were no significant differences be- In terms of marijuana quantity, the three co-use groups that used tween groups for social functioning. both products on the same occasion reported consuming more grams of marijuana on a typical day of use compared to either the cannabis-only group or the concurrent-only group. For example, Comparing the Tobacco/Nicotine-Only Group and the the sequential ϩ coadministration group reported using about a Four Co-Use Groups gram of marijuana when they used, which is a little larger than a bottle cap, compared to about ½ a gram for the cannabis-only and Table 5 contains means and standard deviations for each out- concurrent-only groups. On the CUDIT-SF, the sequential ϩ co- come by co-use subgroup, as well as the overall analysis of administration group reported a mean CUDIT-SF score that was covariance test statistic and significant subgroup differences. higher than the cutoff score of 2, which is indicative of cannabis Tobacco/nicotine use and dependence. A comparison of the use disorder; the score for this group was significantly higher than five mutually exclusive tobacco/nicotine groups found overall for any of the other four groups. group differences on tobacco/nicotine use and dependence. The Marijuana problems. A comparison of the five mutually sequential ϩ coadministration group reported significantly more exclusive cannabis groups found overall differences on each out- frequent cigarette use and e-cigarette use in the past year compared come. For marijuana-related consequences, the three co-use to the tobacco/nicotine-only group and the other three co-use groups that used cannabis and tobacco/nicotine products on the groups. In addition, the sequential-only group reported more fre- This document is copyrighted by the American Psychological Association or one of its allied publishers. same occasion reported greater consequences than the cannabis- quent cigarette use and e-cigarette use than the concurrent-only This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. only group; however, there was not a significant difference in and tobacco/nicotine-only groups. Finally, the coadministration- consequences between the group that had used both products in the only group reported more frequent cigarette and e-cigarette use past year, but never on the same occasion (concurrent use only), than the tobacco/nicotine-only group, and more frequent cigarette and the cannabis-only group. The sequential ϩ coadministration use compared to the concurrent-only group. In terms of quantity of group reported more consequences than the sequential-only, use, the sequential ϩ coadministration group reported higher quan- coadministration-only, and concurrent-only groups. In turn, the tity of both cigarette and e-cigarette use compared to the tobacco/ sequential-only and coadministration-only groups reported more nicotine-only group and concurrent-only group, and higher quan- consequences than the concurrent-only group. For selling mari- tity of cigarette use compared to the sequential-only group. In juana, the three co-use groups that used both products on the same addition, the sequential-only group reported a higher quantity of occasion were more likely to sell the drug compared to the both cigarette and e-cigarette use compared to the concurrent-only cannabis-only group and the concurrent-only group. Considering group, and a higher quantity of e-cigarette use compared to the the means, about 20% of those in the sequential ϩ coadministra- tobacco/nicotine-only group. Even though there was an overall tion group reported selling marijuana compared to only 4% in the effect between groups, post hoc tests revealed there were no mean 8 TUCKER ET AL.

differences between groups on the indicators of cigarette or device (coadministration). The heterogeneity within the population e-cigarette dependence. is important to consider, as some co-use subgroups had higher risk Delinquency, physical health, mental health, and social profiles than others. For example, young adults who co-used functioning. Similar to comparisons for the cannabis-only use cannabis and tobacco/nicotine on the same occasion, or mixed the group, we found overall group differences on delinquency, phys- products in the same device, tended to report higher frequency and ical ailments, physical health, anxiety and depression. For delin- quantity of marijuana or tobacco/nicotine use compared to those quency, those in the sequential ϩ coadministration group reported who used only one product. Of note, we did not see these same greater past year delinquency than all other groups. The increases among young adults who used cannabis and tobacco/ sequential-only group also reported greater delinquency than nicotine on separate occasions only. We did not find that cigarette the tobacco/nicotine-only group. For physical ailments, the or e-cigarette dependence was higher among any of the co-use sequential ϩ coadministration group reported more physical subgroups compared to the tobacco/nicotine-only group; however, ailments than the concurrent-only group. Regarding physical consistent with other work (Peters, Budney, & Carroll, 2012), health, the sequential ϩ coadministration group and the sequential- cannabis use disorder scores were significantly higher in the se- only group reported poorer health than the tobacco/nicotine-only quential ϩ coadministration group compared to the cannabis-only group and the concurrent-only group. For both anxiety and depres- group. We found a similar pattern for marijuana consequences, sion, the sequential ϩ coadministration group reported greater marijuana problems (selling the drug, driving after using it), and symptoms than the concurrent-only group. There were no signif- most domains of young adult functioning. Overall, youth who icant differences between groups for social functioning. reported coadministration and sequential use, either alone or in combination, also reported poorer outcomes compared to youth Discussion using only one product or using both products independently. There is some literature on psychosocial and physical health cor- Studies have shown that cannabis and tobacco/nicotine use are relates of co-use in young adults (Masters, Haardörfer, Windle, & highly comorbid in young adulthood (Schauer et al., 2015); how- Berg, 2018; Ramo et al., 2012); however, further longitudinal ever, little research has provided detailed information on how these research is needed to examine how outcomes may differ across substances are used together. This study is among the first to types of co-use over time and to identify mechanisms underlying examine unique combinations of cannabis and tobacco/nicotine these differences. For example, differences across types of co-use use and different types of co-use behaviors in a diverse sample of may be due to the manner in which cannabis and tobacco/nicotine young adults. We found that the most popular forms of both are co-used, characteristics of the person who chooses to co-use in sequential use (using one product right after another) and coad- a particular way, or other factors. Additional research on co-use is ministration (mixing the products) involved smoking combustible also needed to inform various stakeholder groups, including poli- products (i.e., cigarettes, joints, bongs, blunts). Vaping methods cymakers and public health officials, and to guide both tobacco for co-use of cannabis and tobacco/nicotine were somewhat less and cannabis regulatory science (Schlienz & Lee, 2018). prevalent, as noted in prior work (Meier & Hatsukami, 2016), but It is clear from this study and others (Agrawal et al., 2012; may grow in popularity over time given the recent alarming Meier & Hatsukami, 2016; Ramo et al., 2012) that any research increase in vaping among high school students (Cullen et al., study assessing the effects of cannabis or tobacco/nicotine use 2018). Combustible cigarette use has declined substantially over (e.g., whether use contributes to poor physical and mental health) the past 50 years (Lauterstein et al., 2014; National Center for should also account for co-use of these products given the preva- Chronic Disease Prevention and Health Promotion Office on lence of this behavior among young adults. Given the changing Smoking & Health, 2014). However, our study shows that despite legal landscape of cannabis (D’Amico, Tucker, Pedersen, & Shih, these declining rates, the highest rates of cannabis and tobacco/ 2017), and the fact that co-use is associated with more frequent and nicotine co-use are through combustible methods. Though the problematic use, poorer mental and physical health, and delinquent long-term health effects of vaping nicotine (with or without can- behaviors such as getting fired from a job or getting in trouble with nabis) are still being actively studied without firm conclusions the police, it will be important for programming to include content (Budney, Sargent, & Lee, 2015; Giroud et al., 2015; Pisinger & and discussions geared toward co-use of both products, and how Døssing, 2014), vaping is almost certainly a less harmful variant of co-use may also lead to problems. This document is copyrighted by the American Psychological Association or one of its allied publishers. substance use than smoking combustible products (National Acad- This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. emies of Sciences & Medicine, 2018). Findings emphasize the Limitations continued need for early education programs to address the dan- gers of smoking combustible products, and interventions for those Data were collected in a state where medical cannabis had been that have already begun smoking to prevent adverse health effects. legal for about 20 years, mostly (but not exclusively) prior to the Mixing cannabis and tobacco is prevalent in several countries retail sale of recreational cannabis going into effect in January but has generally been considered to be rare in the United States 2018. The use of this predominantly California-based sample (Winstock, Barratt, Ferris, & Maier, 2017). Thus, another interest- limits generalizability of findings; however, the use of such a ing finding from this study is that the majority of young adults who sample allowed us to have a diverse sample of young adults (74% co-use cannabis and tobacco/nicotine products use them together of youth who reported cannabis use were non-White) and offered in some way. Among those who reported using both cannabis and some standardization of both cannabis and tobacco state policies tobacco/nicotine products in the past year, nearly one half had used applied to all participants in the study. Though this study repre- the two products one after the other on the same occasion (sequen- sents the most detailed effort to collect information on specific tial use) and about one third mixed them in the same delivery types of co-use products, our online survey methods relied on CANNABIS AND TOBACCO/NICOTINE CO-USE 9

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