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Underage Cannabis Use Becomes More Common After Legalization, Study Finds

By Alexander Beadle

Published: Jun 06, 2022   
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Young people are more likely to begin using cannabis once recreational cannabis laws are passed in their state, a new study published in Addiction has found.

Contrary to other reports on youth drug use, the researchers at the University of California San Diego also found the same to hold true for underage adolescents initiating cannabis use in these states.

In light of their findings, the researchers believe that more long-term research into both adult and youth cannabis use patterns should be carried out in order to give policy makers and public health experts more context surrounding the implementation of recreational cannabis laws (RCL).

Adults and youth are more likely to begin using cannabis after legalization

The study utilized survey results generated by waves 3 and 4 of the Population Assessment of Tobacco and Health (PATH) Study. In total, responses from around 7,000 youths between the ages of 12 and 20 and 15,000 adults aged 21 and over were examined in this analysis.

Four US states – California, Massachusetts, Nevada, and Maine – implemented recreational cannabis laws between waves 3 and 4 or at the very beginning of wave 4 of the PATH study. Responses from residents in these four states were compared against respondents from other states where cannabis was still completely prohibited and/or where only medical cannabis laws (MCL) had been enacted, in order to study the effects of recreational legalization.

The researchers found that recreational cannabis legalization was associated with greater odds of adult non-users becoming cannabis users, as compared to states with no legal cannabis provisions. This observation held true when compared to the wider group of comparison states containing both the medical-only cannabis use laws or no legal cannabis use laws at all. Additionally, adults were also more likely to transition from being non-users to weekly users of cannabis following legalization.

Worryingly, a similar increase in the odds of transitioning from being non-users to users were also seen in the youth demographic, despite these respondents being too young to legally access cannabis under the new recreational cannabis laws.

“Our findings provide useful information to policymakers and public health practitioners interested in understanding the consequences of legalizing recreational cannabis,” principal investigator Yuyan Shi, an associate professor at the Herbert Wertheim School of Public Health and Human Longevity Science at UC San Diego, said in a statement.

“It’s especially concerning that increased cannabis use occurs among young people because of the detrimental health effects associated with cannabis use at a young age, including impaired respiratory function, cardiovascular disease and adverse effects on mental health.”

No significant associations were seen between recreational legalization and youth non-users becoming weekly users, or when compared to MCL states alone.

More work needed to determine associations between legalization and use

Given the nature of the survey data used in this study, the UC San Diego researchers are careful to warn that their results cannot be interpreted as causality. However, more research could be done that would address some of the limitations of this study and provide policymakers with even more information to work with.

For example, the researchers point out that the cannabis use questions in the PATH study are very broad and don’t require respondents to record what cannabis product types they predominantly use. Given the growing popularity of legal cannabis edibles and vapes in recreational use states, the research group say that this could be examined further.

Similarly, though the PATH study is designed to be representative of the population at the national level, using these data to study state-level trends is likely to be less representative. It is possible that a different data source may provide a more complete picture of these trends.

The study does have several unique strengths. The study is the first to use nationally representative data to estimate individual-level changes following recreational cannabis legalization, and is one of the first to make comparisons against MCL-only and prohibition states individually.

The fact that increasing associations in cannabis use were not seen when compared to MCL-only states could also suggest that RCL has no additional impacts on top of pre-existing MCL laws, the researchers suggest.

“It is worth noting that most of the previous research used MCL and non-legalizing states combined as comparison states and interpreted observed associations as evidence for the impacts of RCL,” the researchers wrote. “We could also adopt this interpretation, but would like to leave the discretion to readers.”

The consequences of youth cannabis use

Whether cannabis legalization encourages youth cannabis use or not is still an open question.

One study that claimed to find no link between legalization and adolescent use was recently retracted and later corrected after concerns were raised about overlap between the two data sets used in the study. After correction, the researchers still found no link between legalization and encouraging cannabis use. However, the earlier secondary finding – that legalization may in fact lead to a small decline in use – was no longer significant.

While some reviews have found that cannabis policy liberalization does not appear to result in any significant change in youth cannabis use, other studies suggest that cannabis use is growing within demographics with historically low cannabis use rates. The increased advertising of cannabis products has also been linked to sharp increases in youth cannabis use.

Teenage cannabis is a particular concern for scientists and lawmakers given the potentially severe health effects of consuming large amounts of cannabis while the brain is developing. Recent studies have indicated that youth cannabis use can affect the development of brain regions associated with decision making, planning, and self-control, while other studies suggest that teens are also generally more sensitive to the impairing effects of THC than their adult counterparts.


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