UF study finds teens’ likelihood of trying marijuana peaks at ages 16, 18

June 29, 2016
Jill Pease

The likelihood adolescents will try marijuana rises steadily from age 11 to age 16, then decreases before hitting another peak at age 18, according to a new University of Florida study.

The study findings, which appear in the American Journal of Drug and Alcohol Abuse, may help experts develop new marijuana prevention strategies, says lead author Xinguang (Jim) Chen, M.D., Ph.D., a professor in the department of epidemiology in the UF College of Public Health and Health Professions and the UF College of Medicine, which are both part of UF Health.

“Many existing marijuana intervention programs target students age 15 and older,” Chen said. “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.”

As medical marijuana laws are passed in more states, there is concern among some experts that adolescents may view marijuana as a substance that can be used safely by anyone, regardless of whether it is part of a treatment plan under a physician’s supervision. Using marijuana at a young age could put adolescents at risk for cognitive problems, according to the National Institute on Drug Abuse. Teens who use marijuana may have impaired brain development and lower IQ. They may receive lower grades and are more likely to drop out of high school.

The UF study was designed to learn when adolescents are most at risk for starting marijuana use. It is one of the first studies to examine the likelihood of marijuana initiation as a function of age and it used a study method called survival analysis that is more sensitive to fluctuations across age groups, Chen said. The team analyzed data from the 2013 National Survey on Drug Use and Health, a nationwide cross-sectional survey including approximately 27,000 respondents ages 12 to 21, sponsored by the Substance Abuse and Mental Health Services Administration.

The researchers found the likelihood that adolescents would start using marijuana climbed steadily starting at age 11, reaching a first peak at age 16. But the researchers were surprised to discover that at age 17, there was a dip in the possibility that teens would start using marijuana. The team theorizes that many 17-year-olds are focused on improving grades and preparing for college entrance exams, which could pull their attention away from experimenting with drugs. This finding may represent an additional approach for developing interventions, Chen said.

“Increasing adolescents’ academic responsibilities and placing more emphasis on education could be one way to postpone drug use initiation, ultimately preventing drug use,” he said.

The likelihood of marijuana initiation rebounded at age 18 for a second peak. This corresponds to another major milestone in the lives of many young adults, said Bin Yu, M.D., M.P.H., one of the study’s co-authors, and a research assistant in the UF department of epidemiology.

“At 18, many adolescents leave their parents’ homes to start college or enter the workforce,” Yu said. “They may be more susceptible to influence from peers and they have less monitoring by their parents and the community.”

The researchers found that by age 21, 54 percent of young adults will have used marijuana.

The research team, which also included Sonam Lasopa, Ph.D., a recent graduate of the UF doctoral program in epidemiology, and Linda B. Cottler, Ph.D., M.P.H., a dean’s professor, chair of the UF department of epidemiology and PHHP’s associate dean for research, noted a second surprise finding when they analyzed the likelihood of marijuana use by race. Adolescents who self-identified as having a multiracial background were significantly more likely to use marijuana than any other racial or ethnic group.

More research is needed to understand the reasons why adolescents from multiracial backgrounds may be at increased risk for initiating marijuana use, Chen said. With that knowledge, experts can develop prevention programs that take into account racial and ethnic differences, as well as age.

“This study finding supports the idea of precision intervention,” he said. “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.”

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