Cannabis Science

Study suggests minimum age for smoking weed should be 19

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As you may already know, in the United States, the minimum age for using marijuana is 21 where it is legal. In Canada, where marijuana is fully legal, the minimum age is the same for alcohol consumption, which is age 18 or 19 depending on the providence. Ages 18, 19, 21 and 25 are the ages usually debated as the minimum legal age. On one hand, there are also tons of articles cautioning teenagers against using marijuana because there could be some issues associated with adolescent cannabis use. However, according to a recent study, the minimum age for using weed should be 19. Here’s why researchers came to that conclusion.

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Why some researchers believe the minimum age for using marijuana should be 19

According to a Canadian study, 19 is the optimal age for those who are using weed recreationally. Their research aimed to look at later life outcomes, how that relates to when people first started using cannabis, and what that should mean for the minimum legal age.

The researchers used data from the Canadian Tobacco Use Monitoring Surveys (CTUMS) which were conducted between 2004 and 2012. They also used the biennial Canadian Tobacco, Alcohol and Drugs Survey (CTADS) conducted in 2013 and 2015. The study itself had a study sample of 21-65. However, the researchers were primarily concerned with the first time users. Therefore, they grouped the ‘first use’ groups as follows: < 18, 18, 19–20 and 21–24 years. It should be noted that those who used cannabis only used it once.

Age 19 was concluded as the optimal age and the reasons are because age 19 is associated with better health both generally and mentally as well as higher educational achievement. The stats they used to justify the minimum age of 19 are: “for mental health, effect size of first using cannabis at age 19–20 (2.8%) was twice as large as that for first using it at age 18 but was not much different from first using it at age 21–24. This lends support to our choice of 19 as MLA for mental health.”

Other results of the study 

While the study concluded that 19 is the best minimum age, there were a number of other interesting findings.

The dangers of having the minimum age before 19

The study found that there is a higher chance of someone using cigarettes if they started using marijuana before the age of 19. According to the study, “the prevalence of cigarette smoking among those who first used cannabis at age 19–20 was 34% lower compared with 28% prevalence of cigarette smoking among those who first used cannabis before 18.” The study explained that the findings reflect “the greater influence of individual characteristics during adolescence (such as risk-taking, sensation seeking and peer influence)”.

Advantages of having the minimum age at 18

Interestingly, the study also believes that the minimum age at 18 has better general health outcomes. The reason behind this, the researchers believe, is that those using cannabis before age 18 use cannabis as a gateway drug for other illicit drugs. The argument is that if the minimum age was 18, people would go to dispensaries instead of the underground market, where other illicit drugs are sold.

Merits for the minimum age being 21

The study did say that there was some merit to the minimum age being 21. There is a lower educational attainment associated with those who use cannabis before the age of 21. The study says, “educational outcomes were 16% higher among those who first used cannabis at age 21–24 relative to those who first used it before age 18.” 

The study stated several possible reasons for this finding, “the lower education attainment associated with initiating cannabis before 21 may be a result of poor neurological and cognitive development due to early cannabis use. It is also possible that as the majority of the students complete university around age 21, using cannabis before that age might lead to higher dropout rate.”

It also noted that the medical community recommends 21 or 25 “based on neuroscientific evidence about adverse impacts of cannabis on cognitive development”. However, the study didn’t find that there was much difference between those who started at age 19 versus those who started later on. In addition to that, there is an added issue of the underground market. According to the study, “policymakers have decided on a lower MLA (minimum legal age) such as 18 or 19 to curb the size of the underground market, but this raises concerns about adverse outcomes for adolescents.”

What others had to say about the study 

Susan Weiss, PhD, director of the division of extramural research at the National Institute on Drug Abuse, was quoted in Healthline saying that the brain doesn’t fully develop until age 25. However, she also made the point that “policy making is difficult because it’s not only public health based. If you push everyone into the black market, you’re not necessarily gaining anything.”

Healthline noted that Linda Richter, PhD, Director of Policy Research and Analysis at the Center on Addiction mentioned in her research that those who use marijuana before age 21 are twice as likely to get marijuana use disorder. The risk remained elevated until age 25. Dr. Richter disagrees with the minimum age being 19 and was quoted in Healthline saying, “Although it is not realistic in our current legal, political and cultural climate, scientific research largely suggests that the optimal age of legalization to protect the public health would be 25 or later, not 19 or younger.”


The study came to the conclusion that age 19 is the best minimum age for non-medical cannabis use. While 19 seems to be much better than 18 and under when it comes to mental health and educational attainment, some express concern about what a minimum age of 19 means for public health. There are merits on both sides of the argument. Furthermore, more research could provide much needed information and possible solutions to the problems associated with each minimum age debated.


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].