Abstract
Introduction and Aims
Cannabis use is the most widely used illicit substance in the United States (US). Currently, over half of US jurisdictions have legalised medical cannabis and nine US jurisdictions (and Washington DC) have legalised non-medical cannabis. Comparisons across jurisdictions can help to evaluate the impact of these policies. The current study examined patterns of cannabis use among youth in three categories: (i) states that have legalised non-medical cannabis with established markets; (ii) jurisdictions that recently legalised non-medical cannabis without established markets; and (iii) all other jurisdictions where non-medical cannabis is prohibited.
Design and Methods
Data come from an online survey conducted among 4097 US youth aged 16–19 recruited through a commercial panel in July/August 2017. Regression models were fitted to examine differences between regulatory categories for cannabis consumption, perceived access to cannabis, modes of use, perceptions of harm and cannabis-impaired driving. All estimates represent weighted data.
Results
States that had legalised non-medical cannabis had higher prevalence, easier access, and lower driving rates than non-legal states. There were few differences between states with established non-medical cannabis markets and those that had recently legalised.
Discussion and Conclusions
Cannabis use among youth was higher in states that have legalised non-medical cannabis, regardless of how long the policy had been implemented or whether markets had been established. This suggests that differences between states with and without legal non-medical cannabis may partly be due to longer-term patterns established prior and highlights the importance of longitudinal evidence to evaluate the impact of cannabis policies.
Keywords: Cannabis, Marijuana, Drug Regulations, Legal Status, Youth
INTRODUCTION
Cannabis is the most popular illicit substance in the United States (US) and youth and young adults are among the highest users of cannabis in the US [1]. The use of cannabis at a young age is associated with negative outcomes such as poor academic achievement and driving whilst under the influence [2–5].
Cannabis remains an illicit substance in the US at the federal level. However, various US jurisdictions have liberalised cannabis policies including both medical and non-medical cannabis. At the time of the current study, four states had an established non-medical cannabis market, Alaska, Colorado, Oregon and Washington, and four states had passed legislation for a new non-medical market yet awaited implementation; California, Maine, Massachusetts and Nevada. The District of Columbia (DC) had legalised cannabis possession and allowed adults to grow their own plants; however, a non-medical market was not permitted. Non-medical cannabis markets in all other states was prohibited.
Public opinion in favor of cannabis legalisation in US has recently increased [6]. However, implementation of more permissive cannabis regulations have brought concerns of increased use, lower harm perceptions and increased cannabis-impaired driving among youth due to permissive norms and broader access [7,8]. Previous research on the comparison between youth cannabis use before and after medical cannabis laws are inconsistent, with some concluding an increase in use, and some no change [7,9]. Evidence on the impact of cannabis legalisation remains preliminary given that the regulation changes have only recently been implemented. In addition, the transition to a legal marketplace does not occur immediately upon legalisation; indeed, it typically requires one to two years to fully establish ‘legal’ retail stores in states that have legalised non-medical cannabis. For this reason, the first US states to legalise non-medical cannabis—Colorado and Washington State, in 2012— have received particular attention. Data on patterns of cannabis use in Colorado and Washington State have yielded mixed findings to date [10–13]. Both states have seen a decrease in the perceptions of harm from cannabis use; however, this has been an overall trend across the US in the past few decades [14]. Previous research has shown that perception of harm is a potential indicator of cannabis use, and that a reduction of perceived harm is commonly associated with an increase in cannabis use [15]. Furthermore, this association has been seen to be bidirectional and that cannabis use influences perception of harm [16].
The current study examined patterns of youth cannabis use across three categories: (i) Established Non-Medical Cannabis Markets (NCM)—states that have legalised non-medical cannabis and have an established market (Colorado, Washington, Alaska, Oregon); (ii) New NCMs—jurisdictions that recently legalised non-medical cannabis without established markets (California, Maine, Massachusetts, Nevada); and (iii) Prohibited NCMs—all other jurisdictions where non-medical cannabis is not legal. This study examined differences between these jurisdictions on five primary outcomes among youth: prevalence of use, perceived access to use, modes of use, perception of harm, and cannabis-impaired driving. We hypothesised closer similarities in outcomes in Established and New NCMs in comparison to Prohibited NCMs.
METHODS
Study design
Data are from Wave 1 of the International Tobacco Control Policy Evaluation Project Tobacco and Youth E-cigarette Survey, conducted in Canada, England and the United States [17]. Data were collected via self-completed web-based surveys conducted in July/August 2017 with youth aged 16 through 19. Respondents were recruited through Nielsen’s Consumer Insights Global Panel and their partners’ panels, either directly or through their parents. Email invitations (with a unique link) were sent to a random sample of panelists (after targeting for age criteria); panelists known to be ineligible were not invited. A restriction on small screen size was applied to ensure that images presented in the survey could be viewed with a minimum amount of scrolling. The survey was conducted in English in all countries, as well as French in Canada, and took approximately 15 minutes to complete. The same survey measures were used in all countries, with the exception of race/ethnicity, region, and education questions, which were based on census questions in each country. Respondents provided consent prior to completing the survey. Respondents received remuneration in accordance with their panel’s usual incentive structure (e.g. points-based or monetary rewards, chances to win prizes).
Measures
Survey measures were drawn from existing national surveys [18] and adapted for the current study. In all cases, participants had the option of selecting ‘Don’t Know’ or ‘Refused’.
Sociodemographic
Socio-demographic measures included state of residency (“Prohibited NCMs”/“New NCMs”/“Established NCMs”), sex at birth (“male”/“female”), and age at time of survey. Ethnicity was recoded into “white” vs. “non-white”. Due to the age of participants, education was not included given the multicollinearity with age. Income was captured by the number of computers in their home [19,20].
Cannabis consumption
All youth were asked: “When was the last time you used marijuana/cannabis?” (“I have never used cannabis”/“Earlier today”/“Not today but sometime in the past week”/“Not in the past week but sometime in the past month”/“Not in the past month but sometime in the past 6 months”/“Not in the past 6 months but sometime in the past year”/“1 to 4 years ago”/“5 or more years ago”). Responses were recoded into “Never” vs. “Used, but not in the last month” vs “Used in the last month”. Don’t Know” and “Refused” responses were treated as missing.
Modes of Use
All youth who reported to have used cannabis in the last month were asked: “In the last 30 days, did you…” Answers were a “Yes” vs. “No” checklist to the following options: Smoke cannabis without tobacco/Smoke cannabis with tobacco/Use a waterpipe or bong to smoke cannabis/Use a vapouriser to heat dried cannabis/use an e-cigarette to vape cannabis/Eat or drink cannabis in a food or drink/Use cannabis extracts.
Perceived Access to Cannabis
All youth were asked “How difficult do you think it would be for you to get cannabis, if you wanted?” (“Very difficult”/“Fairly difficult”/“Fairly easy”/“Very easy”). Answers were collapsed into “Difficult” vs. “Easy”. Don’t Know” and “Refused” responses were treated as missing.
Perceptions of Harm
All youth were asked “How much do you think people harm themselves when they SMOKE marijuana/cannabis?” (“No harm”/“Little harm”/“Some harm”/“A lot of harm”). Answers were collapsed into “A lot of harm” vs. “Other” (No harm/Little harm/Some harm/Don’t know).
Youth who answered that they had used cannabis before were asked “Are you worried that using marijuana/cannabis will damage your health in the future?” (“Not at all”/“A little”/“Moderately”/“Very”). Answers were collapsed into “Not at all worried” vs.”Other” (A little/Moderately/Very/Don’t know).
All youth were asked “How much do you think people risk harming their mental health when they use marijuana/cannabis on a regular basis?” (“No”/“Slight”/“Moderate”/“Great”). “Refused” was removed. Answers recoded into “Great risk” vs. “Other” (No/Slight/Moderate/Don’t know).
Driving after Cannabis Use
Youth who answered that they had used cannabis before were asked, “Have you ever driven a car or other vehicle within two hours of using marijuana/cannabis?” (“No, never”/“Yes, in the last 30 days”/“Yes, more than 30 days ago”). All youth were also asked, “To your knowledge, have you ever been a passenger in a car or other vehicle driven by someone who had been using marijuana/cannabis in the last two hours?” (“No, never”/“Yes, in the last 30 days”/“Yes, more than 30 days ago”). Answers to both questions were recoded into “No, never” vs. “Yes” (In the last 30 days/More than 30 days ago). Don’t Know” and “Refused” responses were treated as missing.
All youth were asked, “Do you think driving a car or other vehicle within two hours of using marijuana/cannabis increases the risk of getting into an accident?” All respondents were also asked “If someone drives a car or other vehicle within two hours of using marijuana/cannabis, how likely are they to get caught by the police?” Response options for both questions were “Not at all”/“A little”/“Somewhat”/“A lot”, which were recorded into “A lot” vs. “Other” (Somewhat/A little/Not at all/Don’t know).
Statistical analysis
A total of 13,468 youth completed the survey and consented to the use of their data. After removing participants who provided incomplete or invalid data on smoking status, e-cigarette use, or other variables used for weighting (n=1022), as well as respondents who provided an incorrect response to a data quality check question (n=382), a total of 12,064 respondents were retained for the analytic sample. A sub-sample of US youth (n=4097) were included in the current analysis. As shown in Table 1, 3328 youth were from Prohibited NCMs, including eight participants from the District of Columbia; 544 youth were from New NCMs (California, Maine, Massachusetts, Nevada); and 207 youth were from Established NCMs (Alaska, Colorado, Oregon, Washington).
Table 1.
Unweighted (left) and weighted (right) sample characteristics by cannabis market in the United States (2017).
| Unweighted respondents (n=4079) | Weighted respondents (n=4079) | |||||||
|---|---|---|---|---|---|---|---|---|
|
| ||||||||
| Prohibited states, % (n=3350) | New non-medical states, % (n=536) | Established non-medical states, % (n=193) | P-value for χ2 | Prohibited states, % (n=3328) | New non-medical states, % (n=544) | Established non-medical states, %(n=207) | P-value for χ2 | |
| Sex | 0.353 | 0.040 | ||||||
| Female | 60.1 (2012) | 60.5 (324) | 65.3 (126) | 46.2 (1539) | 46.3 (252) | 55.3 (114) | ||
| Male | 39.9 (1338) | 39.6 (212) | 34.7 (67) | 53.8 (1790) | 53.7 (292) | 44.7 (92) | ||
| Age, years | 0.309 | 0.774 | ||||||
| 16 | 21.8 (731) | 20.5 (110) | 22.3 (43) | 22.9 (761) | 24.3 (132) | 21.5 (45) | ||
| 17 | 22.9 (768) | 18.8 (101) | 20.7 (40) | 24.3 (808) | 21.0 (114) | 23.5 (49) | ||
| 18 | 30.4 (1018) | 34.7 (186) | 32.1 (62) | 29.7 (987) | 30.8 (168) | 30.1 (62) | ||
| 19 | 24.9 (833) | 25.9 (139) | 24.9 (48) | 23.2 (772) | 24.0 (130) | 24.9 (51) | ||
| Ethnicity | <0.001 | 0.008 | ||||||
| White | 75.4 (2527) | 63.1 (338) | 76.2 (147) | 79.6 (2650) | 75.0 (408) | 84.5 (175) | ||
| Non-white | 24.6 (823) | 36.9 (198) | 23.8 (46) | 20.4 (678) | 25.0 (136) | 15.5 (32) | ||
| No. of computers | 0.565 | 0.036 | ||||||
| None or one | 9.6 (319) | 9.6 (51) | 6.3 (12) | 10.6 (351) | 8.9 (48) | 4.7 (10) | ||
| Two | 19.3 (640) | 18.0 (95) | 20.3 (39) | 21.0 (693) | 19.1 (103) | 23.7 (49) | ||
| More than two | 71.1 (2362) | 72.4 (383) | 73.4 (141) | 68.4 (2253) | 72.0 (387) | 71.6 (148) | ||
Sample weights were constructed using a raking algorithm. First, respondents were divided into three cigarette smoking categories: never smokers, experimental smokers, and current/former smokers. Raking was then performed based on geographic region, language in Canada, and the following cross-classifications: sex by smoking, age by smoking, and age by race/ethnicity in the US. Finally, weights were rescaled to sample size within each country/condition, to allow for comparisons between countries with different population sizes.
Estimates reported are weighted unless otherwise specified. All models were adjusted for country, age, sex, ethnicity, and number of computers in the home. Respondents were excluded from analyses for measures with missing data. Analyses were conducted with SAS 9.4.
Sample characteristics were examined, and chi-squared tests were used to assess differences across US jurisdictions. Multinomial logistic regression models were fitted to examine differences in the prevalence of cannabis use between regulatory ‘conditions’ (Established NCMs, New NCMs and Prohibited NCMs). Binary logistic regression were fitted to examine any differences between regulatory conditions for each of four outcomes: modes of use, perceived access to cannabis, perceptions of harm, and driving after using cannabis.
Ethics
This study has been reviewed and received ethics clearance through a University of Waterloo Research Ethics Committee (ORE#21847) and the King’s College London Psychiatry, Nursing and Midwifery Research Ethics Subcommittee (PNM RESC).
RESULTS
Table 1 shows unweighted and weighted sample characteristics in each US category (n=4097).
Cannabis Consumption
Table 2 indicates the prevalence of cannabis use in each US category. Overall, the majority of youth in Prohibited, New and Established NCMs had never used cannabis (70.9%, 65%, 63%, respectively). Youth in Prohibited NCMs were significantly less likely to have used cannabis in the last month (vs. never), than youth in New NCMs (adjusted odds ratio [AOR] = 0.69, 95% confidence interval [CI] 0.53,0.89, P=0.005) or Established NCMs (AOR=0.59, 95% CI: 0.40,0.86, P=0.006). Findings were inconclusive between all regulatory conditions regarding cannabis use more than a month ago (vs. never).
Table 2.
Weighted outcome variables by cannabis market in the United States (2017).
| Respondents used in analysis (n=4079) | ||||
|---|---|---|---|---|
| Prohibited states, % (n=3328) | New non-medical states, % (n=544) | Established non-medical states, % (n=207) | P-value for χ2* | |
| Consumption measures | ||||
| When was the last time you used cannabis? | 0.003 | |||
| Never | 70.9 (2294) | 64.9 (348) | 63.2 (129) | |
| Used, but not in the last month | 15.8 (510) | 17.5 (94) | 16.5 (34) | |
| Used in the last month | 13.3 (431) | 17.6 (94) | 20.3 (42) | |
| Modes of use (In the last 30 days, did you…)** | ||||
| Smoke cannabis WITHOUT tobacco? | 0.249 | |||
| Yes | 89.9 (383) | 92.5 (85) | 97.1 (40) | |
| No | 10.2 (43) | 7.5 (7) | 2.9 (1) | |
| Smoke cannabis WITH tobacco in a joint or blunt? | 0.273 | |||
| Yes | 32.7 (138) | 30.6 (28) | 20.5 (8) | |
| No | 67.3 (285) | 69.4 (64) | 79.5 (33) | |
| Use a waterpipe/bong to smoke cannabis? | 0.041 | |||
| Yes | 52.9 (227) | 66.9 (62) | 59.7 (25) | |
| No | 47.1 (202) | 33.1 (31) | 40.3 (17) | |
| Use a vapouriser to heat dried cannabis leaves or herb? | 0.717 | |||
| Yes | 22.4 (96) | 18.6 (17) | 22.8 (9) | |
| No | 77.6 (331) | 81.4 (75) | 77.2 (30) | |
| Use an e-cigarette to vape cannabis oil or liquid? | 0.032 | |||
| Yes | 24.2 (103) | 27.8 (26) | 43.1 (17) | |
| No | 75.8 (324) | 72.2 (67) | 56.9 (22) | |
| Eat or drink cannabis in a food or a beverage? | 0.099 | |||
| Yes | 26.2 (112) | 32.2 (30) | 40.4 (17) | |
| No | 73.8 (316) | 67.8 (63) | 59.7 (25) | |
| Use cannabis extracts, including oil, wax or shatter? | <0.001 | |||
| Yes | 23.9 (103) | 34.8 (32) | 48.0 (20) | |
| No | 76.1 (327) | 65.3 (60) | 52.0 (23) | |
| Access | ||||
| How difficult do you think it would be for you to get cannabis, if you wanted? | <0.001 | |||
| Difficult | 41.1 (1230) | 33.1 (167) | 32.1 (61) | |
| Easy | 58.9 (1764) | 66.9 (337) | 67.9 (130) | |
| Perceptions of harm | ||||
| How much do you think people harm themselves when they SMOKE cannabis? | 0.188 | |||
| A lot of harm | 28.5 (947) | 25.2 (137) | 30.9 (64) | |
| Otherwise (Some/Little/No harm/don’t know) | 71.5 (2378) | 74.8 (407) | 69.1 (143) | |
| How much do you think people risk harming their mental health when they use cannabis on a regular basis? | 0.189 | |||
| Great risk | 29.7 (987) | 26.0 (141) | 27.8 (58) | |
| Otherwise (Moderate/Slight/No/Don’t know) | 70.3 (2333) | 74.0 (402) | 72.2 (149) | |
| Are you worried that using cannabis will damage your health in the future?** | 0.102 | |||
| Not at all worried | 67.4 (290) | 55.9 (53) | 63.8 (27) | |
| Otherwise (Little/Moderately/Very/Don’t know) | 32.6 (140) | 44.1 (42) | 36.2 (15) | |
| Cannabis and driving | ||||
| Have you ever driven a car or other vehicle within 2 hours of using cannabis?** | 0.017 | |||
| No, never | 70.7 (650) | 81.0 (148) | 73.9 (54) | |
| Yes | 29.3 (270) | 19.1 (35) | 26.1 (19) | |
| Have you ever been a passenger in a car or other vehicle driven by someone who had been using cannabis in the last 2 hours? | 0.031 | |||
| No, never | 75.8 (2294) | 71.4 (350) | 69.9 (130) | |
| Yes | 24.2 (731) | 28.6 (140) | 30.1 (56) | |
| Do you think driving a car or other vehicle within 2 hours of using cannabis increases the risk of getting into an accident? | 0.845 | |||
| A lot | 43.8 (1454) | 43.7 (237) | 41.8 (86) | |
| Otherwise (Somewhat/Little/Not at all/Don’t know) | 56.2 (1865) | 56.3 (306) | 58.2 (120) | |
| If someone drives a car or other vehicle within 2 hours of using cannabis, how likely are they to get caught by the police? | 0.020 | |||
| Not at all/A little/Don’t know | 50.1 (1663) | 56.6 (308) | 52.1 (108) | |
| A lot/Somewhat | 49.9 (1656) | 43.4 (236) | 47.9 (99) | |
Unadjusted bivariate analyses.
Participants are those who had answered “Yes” to using cannabis in the last month.
Modes of Use
As Table 2 shows, the most common method of cannabis use across Prohibited, New and Established NCMs was smoking cannabis without tobacco (90%, 93%, 97%, respectively). Youth in Prohibited NCMs were significantly less likely to have used a waterpipe/bong to smoke cannabis in the last 30 days than youth in New NCMs (AOR=0.53, 95% CI 0.32, 0.87, P=0.011), with no conclusive findings observed between youth in Prohibited and Established NCMs or New and Established NCMs.
Youth in Established NCMs were significantly more likely to have used an e-cigarette to vape cannabis in the last 30 days than youth in Prohibited (AOR=2.61, 95% CI 1.31, 5.20, P=0.007) or New NCMs (AOR=2.42, 95% CI 1.07, 5.46, P=0.033). Findings were inconclusive between youth in Prohibited and New NCMs.
Youth in Established NCMs were significantly more likely to have eaten or drank cannabis in a food or beverage in the last 30 days than youth in Prohibited NCMs (AOR=2.08, 95% CI 1.06, 4.12, P=0.034). Findings were inconclusive between youth in Prohibited and New NCMs or New and Established NCMs.
Youth in Prohibited NCMs were significantly less likely to have used cannabis extracts including oil, wax or shatter in the last 30 days than youth in New (AOR=0.59, 95% CI 0.35, 0.97, P=0.037) or Established NCMs (AOR=0.29, 95% CI: 0.15, 0.57, P <0.001. Findings were inconclusive between youth in New and Established NCMs.
In addition, no conclusive findings were observed between youth in all regulatory conditions regarding their use of cannabis with or without tobacco, or their use of a vaporiser to heat cannabis leaves.
Perceived Access to Cannabis
As Table 2 shows, approximately two-thirds of youth in New (67%) and Established NCMs (68%) reported that it was easy to obtain cannabis if they wanted compared to 58.9% of youth in Prohibited NCMs. Youth in Prohibited NCMs were significantly less likely to report that it was easy to get cannabis than youth in New (AOR=0.71, 95% CI 0.58, 0.86, P <0.001) or Established NCMs (AOR=0.67, 95% CI 0.49, 0.92, P=0.013).
Perceptions of Harm
Approximately a third of youth in Prohibited, New and Established NCMs reported that people harm themselves “a lot” when they smoke cannabis (28.5%, 25%, 31%, respectively). A similar proportion of youth reported that regular cannabis use presents a “great risk” to mental health (29.7%, 26%, 28%, respectively). Of those who had used cannabis, the majority of all youth were “not at all” worried that cannabis will damage their health in the future, as shown in Table 2. Findings were inconclusive between youth in all regulatory conditions for any perception of cannabis harm questions.
Driving after Cannabis Use
As Table 2 shows, approximately a quarter of youth in Prohibited (29%) and Established NCMs (26%) reported they had ‘ever’ driven a car within two hours of using cannabis, compared to 19% of youth in New NCMs. Youth in Prohibited NCMs were significantly more likely to report having driven a car within two hours of using cannabis than youth in New NCMs (AOR=1.78, 95% CI 1.19, 2.67, P=0.005). Findings were inconclusive between youth in Prohibited and Established NCMs or youth in New and Established NCMs.
Approximately a quarter of youth in Prohibited (24.2%), and New NCMs (29%) had been a passenger in a car driven by someone who had been using cannabis in the last two hours, compared to 30% of youth in Established NCMs. Youth in Prohibited NCMs were significantly less likely to have been a passenger in a car within two hours of the driver using cannabis than youth in New NCMs (AOR=0.78, 95% CI 0.63, 0.98, P=0.029). Findings were inconclusive between youth in Prohibited and Established NCMs or youth in New and Established NCMs.
Approximately half of youth in Prohibited, New and Established NCMs reported that driving a car within two hours of using cannabis increases the risk of an accident by “a lot” (43.8%, 44%, 42%, respectively). Findings were inconclusive between youth in all regulatory conditions.
Approximately half of youth in all regulatory conditions reported that they would be “a lot” or “somewhat” likely to be caught by the police if they were driving a car within two hours of using cannabis. Youth in Prohibited NCMs reported a higher likelihood of getting caught (AOR=1.28, 95% CI 1.06, 1.54, P=0.009) than youth in New NCMs, with no conclusive findings observed between youth in Prohibited and Established NCMs or in New and Established NCMs.
DISCUSSION
Consistent differences in perceptions and patterns of cannabis use were observed between jurisdictions with and without legal non-medical cannabis. Overall, youth were more likely to report using cannabis in states that have legalised non-medical cannabis, similar to prevalence from national surveys. Data from a US survey conducted in 2013–2014 found that the highest rates of youth use were in states that had a ‘new’ or ‘established’ non-medical cannabis market [21]. This survey was conducted before states with a newly legalised market had passed their laws in 2014, suggesting that these states already had higher levels of use than non-legal states. Longitudinal studies conducted on pre and post legalisation in established non-medical cannabis markets have generally shown few changes in cannabis use among youth, which suggests that differences between states with and without legalised non-medical cannabis may be due to pre-existing trends rather than policy changes [10,11,22]. This is similar to what was found pre and post medical cannabis laws [23–25]. The lack of conclusive findings between states with new and established non-medical cannabis markets is consistent with this prior research.
In addition to higher rates of overall use, cannabis users living in legal states were more likely to report consuming cannabis edibles and extracts. These findings are consistent with the proliferation of commercially prepared edibles and extracts that are available in non-medical cannabis retail outlets in states such as Colorado and Washington State. Although the differences between these new and established legal markets were not conclusive, this was largely due to a lack of power due to smaller sample sizes in these regulatory conditions, and the pattern of data is consistent with greater consumption of edibles and extracts in states with established markets [26,27]. However, it is worth noting that, among all jurisdictions, smoking cannabis remains the dominant form of consumption among youth [28].
Youth in states with prohibited markets were less likely to report it was easy to obtain cannabis than youth in legalised states. One could predict that the legalisation of non-medical cannabis would increase youth access by providing more visible and alternate methods, such as storefronts, via advertising or through cultivation in the home [29,30]. Due to the age of participants, youth would not have direct access to the non-medical market; however, in states with established markets, youth have reported increased access [31]. Future research should examine the impact of home cultivation on youth access.
Although it has been suggested that cannabis legalisation will reduce perceptions of risk, no conclusive findings were observed between regulatory conditions for perceptions of physical and mental harm from cannabis use. Most states that have legalised non-medical cannabis have increased public education and mass media campaigns, as one component of their broader cannabis legalisation policy. For example, Washington State and Colorado launched prevention campaigns targeted at youth where they promoted alternative activities to pursue instead of using cannabis [32,33]. While legalisation may have the potential to soften perception of risk among young people, the communication campaigns that have accompanied cannabis legalisation may have attenuated or counteracted any such effect.
Few differences in driving after cannabis use were observed between regulatory conditions. Youth in prohibited states were almost twice as likely to report driving a car within two hours of using cannabis but less likely to have been a passenger than youth in newly legalised states. However, findings were inconclusive between youth in states with a prohibited and established market or with a new and established market. The pattern of findings is similar to the data on perceptions of risk, and may reflect greater public education and enforcement activities in states that have legalised non-medical cannabis. As states have legalised non-medical cannabis, they have also prohibited cannabis-impaired driving with a 5ng/ml threshold of THC in the blood, whereas cannabis impaired laws are inconsistent across prohibited states [34,35]. Most states with prohibited markets have ‘effect-based DUI’ laws which requires proof of recent ingestion. However, proving recent ingestion is not straightforward due to a current lack of a reliable equivalent to the breathalyser for alcohol [35]. Youth in prohibited states were somewhat more likely to report that using cannabis within two hours of driving increases your chances to be caught by the police, than youth in newly legalised states but not in states with an established market, with no conclusive findings between youth in new and established markets. The underlying reason for this pattern of results is unclear. It is possible that the transition to more permissive non-medical cannabis regulations promotes a perception that cannabis is no longer of law enforcement priority, including impaired driving; whereas, this message perception is corrected after the cannabis market has been established and communication campaigns have been implemented [36,37]. Future research should examine changes during this key transition period to examine this possibility.
It should be noted that there are other, larger studies that track cannabis trends, such as Monitoring the Future (MTF) and the National Survey on Drug Use and Health (NSDUH) [38,39]. However, unlike MTF or NSDUH, the current study includes more comprehensive measures of cannabis use that allows us to explore potential differences on a greater number of policy-relevant outcomes.
Limitations
This study has several limitations. Self-report data are subject to memory recall and social desirability biases. Non-medical cannabis remains illegal at the federal level, which may result in underreporting. The sample sizes differ substantially; however, the proportions could be expected from the number and size of the states within each category. Another limitation is that in November 2014, DC had legalised the personal use of non-medical cannabis. However, DC does not have a non-medical retail market in which consumers can lawfully buy non-medical cannabis. Therefore, consumers can only grow cannabis at home or receive it as a gift (where there is no monetary exchange). As such, it was categorised with states that had prohibited markets rather than established legal markets. Supplementary analyses were conducted with DC included with established markets, and conclusions remained the same. Finally, non-probability methods were used to recruit the sample; however, the sample was weighted on region, age, sex, and smoking status to established population benchmarks.
Conclusion
Overall, prevalence of use was somewhat higher in states that had legalised non-medical cannabis, with similar levels of risk perceptions and driving after cannabis use. Relatively few differences were observed between states with an established market and those that only recently legalised, which suggests that differences between legal and non-legal states may be partly due to pre-established trends and a type of ‘self-selection’ effect, in that states that legalise non-medical cannabis typically have higher rates of cannabis use anyway. The findings provide preliminary support for the importance of public education campaigns that typically accompany cannabis legalisation to help shape risk perception. Future research that compares different regulatory conditions using pre-post longitudinal data will help to elucidate the extent to which regulatory changes influence cannabis use among young people.
Acknowledgments
This project has been made possible through a P01 Grant (1P01CA200512-01) from the US National Institutes of Health. Additional support was provided by a Canadian Institutes of Health Research (CIHR) Catalyst Grant (Hammond), a CIHR-Public Health Agency of Canada Applied Chair in Public Health (Hammond), and a Vanier Canada Graduate Scholarship (Wadsworth). The funders had no involvement in project implementation, data analysis or reporting.
Funding
This project has been made possible through a P01 Grant (1P01CA200512-01) from the US National Institutes of Health. Additional support was provided by a CIHR Catalyst Grant (Hammond), a CIHR-Public Health Agency of Canada Applied Chair in Public Health (Hammond), and a Vanier Canada Graduate Scholarship (Wadsworth).
Footnotes
Declarations of competing interest
The funders had no involvement in project implementation, data analysis or reporting, and the authors have no conflicts of interest to declare.
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