Marijuana use may start from age 11, study finds

Marijuana remains the most commonly used illicit drug in the United States, and its use is particularly widespread among adolescents. Now, a new study has identified the ages at which adolescents are most likely to try the drug, which may have implications for current marijuana intervention programs.

According to the National Institute on Drug Abuse (NIDA), last year, around 6.5 percent of eighth-grade students, 14.8 percent of 10th-graders, and 21.3 percent of 12th-graders reported current marijuana use. Among 12th-graders, 6 percent reported using the drug daily.

Marijuana use can pose a number of risks to physical and mental health, including mood changes, altered senses, impaired movement and breathing problems.

Additionally, use of the drug in adolescence may raise the risk of long-term problems, such as poor cognitive functioning; studies have shown that teenagers who use marijuana have a lower IQ and poorer academic outcomes.

Previous research has also indicated that teenagers who use marijuana are more likely to engage in the use of other illicit drugs.

However, NIDA report that adolescent awareness of these risks is gradually decreasing, likely due to increased legalization of marijuana for medical or recreational use across the U.S.

For this latest study, published in the American Journal of Drug and Alcohol Abuse, researchers from the University of Florida (UF) set out to determine the ages at which adolescents are most likely to try marijuana - information that they say could help guide drug prevention programs.

'Drug education needs to start earlier'

Lead author Dr. Xinguang Chen, a professor in the Department of Epidemiology at UF, and colleagues analyzed data from the 2013 National Survey on Drug Use and Health, which included 26,659 participants aged 12-21 years.

The researchers used the data to estimate the risk of marijuana use initiation among the participants from birth.

Overall, the team found that 54 percent of adolescents had started using marijuana by the age of 21.

They found that adolescents are at risk of trying marijuana from the age of 11. This risk steadily increases until the age of 16, at which point it hits a peak, the researchers report.

The authors note that current marijuana intervention programs focus on adolescents aged 15 and older. Based on their results, the authors suggest such programs should be initiated earlier.

"Our findings demonstrate the need to start drug education much earlier, in the fourth or fifth grade. This gives us an opportunity to make a preemptive strike before they actually start using marijuana."

Dr. Xinguang Chen

Marijuana use risk drop at age 17

At the age of 17, the team found that the risk of first-time marijuana use drops. The authors say this could be because teenagers are more focused on their studies and college entrance exams at this age, rather than drug use.

At the age of 18, however, the researchers found the risk of marijuana use initiation hits another peak - a finding they say might be explained by the life changes that occur at this age.

"At 18, many adolescents leave their parents' homes to start college or enter the workforce," says study co-author Dr. Bin Yu, also of UF's Department of Epidemiology. "They may be more susceptible to influence from peers and they have less monitoring by their parents and the community."

On analyzing the risk of marijuana use by race/ethnicity, the researchers were surprised to find it varied; adolescents from a multiracial background were significantly more likely to use the drug than those from other backgrounds.

The authors say future research should investigate why people from multicultural backgrounds may be at greater risk for marijuana use, as well as why certain age groups are at heightened risk.

They believe such information could aid the development of more targeted marijuana prevention programs.

"This study finding supports the idea of precision intervention. Intervention programs should be developed for both parents and adolescents, and delivered to the right target population at the right time for the best prevention effect."

Dr. Xinguang Chen