Early Cannabis Use Poses Risks to Physical and Mental Health

Researchers compared the effects of cannabis on the physical and mental health of teens who started using cannabis before and after age 15. They found that cannabis was neither performance-enhancing nor good for general health and well-being. The data are important because they confirm many other studies warning of the effects of teen cannabis use. But this new study goes further: It examines whether adolescent cannabis use is associated with greater utilization of medical care for mental and physical conditions in young adulthood.

The health issues concern parents, as cannabis legalization has brought cannabis, THC vapes, gummies, and other cannabis products to local neighborhoods and schools. Former Congressman and prevention advocate Patrick J. Kennedy warned in 2018 on The Last Word podcast, "Today's THC drug products are not the marijuana of years ago. They are engineered to maximize potency and hook a new generation of high-frequency users to make huge profits for an industry that relies on addiction to succeed.”

The new JAMA study followed 1,591 participants (51.4% female) from Québec, Canada, from birth to age 23, using Canadian health databases. Self-reported past-12-month cannabis use at ages 12, 13, 15, and 17 were each compared with records of medical care utilization (ages 18–23) for any mental disorder and substance-related disorders, suicide-related behaviors, and any physical health condition, like respiratory diseases, injuries/poisoning, or other physical diseases.

Early adolescent cannabis use correlated with higher mental and physical health care utilization in young adulthood. The findings are in line with my review of past health risks. Teens with later-onset use have more physical but not mental-health signals. The new findings confirm warnings of national experts about the importance of avoiding cannabis in teens, delaying initiation, and reducing the number of exposures.

The new study also questions criticisms of previous self-report-only studies by capturing critical outcomes. Of course, causality cannot be proven. Unmeasured confounding variables like genetics could complicate factors.

The new research emphasizes the need for strategies that delay initiation and reduce intensity, aligning with public health messaging. Pablo Martínez, PhD, McGill, study co-author, said, “Even when we considered several pre-existing risk factors for cannabis use, we still found increasing risks of using healthcare services for mental and physical health problems for youth with early-onset cannabis use. That suggests cannabis itself may play a role.”

Which psychiatric or medical diagnoses result are not defined. But among early/frequent cannabis users, the physical health emergencies, emergency department visits, injuries, poisoning, and other physical problems were elevated.

The reality: If cannabis were a medicine, it would be considered dangerous until proven safe and effective. For teens, cannabis use is a challenge to or stress on the developing body and brain. Early or frequent use is a high-risk pathway, increasing odds of later mental and physical morbidity requiring care.

Consistent with the data from McGill University researchers, the Canadian Centre on Substance Abuse (CCSA) reports, "Early-onset cannabis use has a tremendous impact on the structure and functioning of the teenage brain and can weaken the foundation for future life success.”

Take-home message for parents and pediatricians is that prevention is critical. First use should be delayed as long as possible. Frequent use should precipitate an evaluation. Any screening should specifically ask about age at first use, as well as frequency. Along with the harm reported in the JAMA study, cannabis use is also linked increasingly to fatal car crashes.

Numerous previous research studies have reported (2019–2025) that early and/or heavy adolescent cannabis use is associated with an elevated risk of later mental-health problems, cognitive effects, and health service utilization. A major longitudinal study showed that cannabis use in adolescence is associated with depression and suicidality in adult life. It also showed that the younger age at first use and the higher the frequency of adolescent use, the more markedly increased the risk —mirroring the JAMA report.

Cannabis is well-known to reduce anxiety about achievement or testing, but it may do so by interfering with working memory. In a recent JAMA study of working memory/brain function among about 1,000 young adults, recent and heavy lifetime cannabis use was associated with reduced brain activation during working-memory tasks. This may be the mechanism underlying academic/functional impairment found in the new study.

Adolescence Essential Reads

Tell Your Teenager to Go to Bed

How the Pandemic Changed Puberty for Girls

Adolescent use is reported to cause cognitive impairments, depression, and psychosis risk, and while there is often some uncertainty around causality, converging evidence suggests earlier initiation and heavier exposure carry significant risk. Cannabis is not an antidepressant.

A long list of respected researchers, from Nora Volkow, M.D., head of the National Institute on Drug Abuse, to Yale’s Herbert Kleber, M.D., to Harvard’s Kevin Hill, M.D., to Mt Sinai’s Yasmin Hurd, Ph.D. to Surgeon General Vivek Murthy, M.D., have warned about legalization-related harms resulting from changes in cannabis access, THC concentration , perceived harm, and the increased risks for teens, many of whom may be under the false impression that cannabis use is safe for them.

Screen Adolescents

Precise screening of teens is warranted. Instead of asking, "Do you use cannabis?" ask, "At what age did you first try cannabis?" "What do you use? " "When and how often do you use now (daily/near-daily)?" Remember to ask about edibles. If the person has not used cannabis, they will say so.

Pay special attention to early initiation of use and regular or frequent use in teens. That raises red flags, and monitoring or intervention may be required.

Incorporate counseling on marijuana intoxication-related injuries in driving, sports, and falls; poisoning with edibles; and respiratory toxicity of smoked forms. “Delay initiation, reduce intensity” is consistent with the evidence arc and the authors’ conclusions—and resonates with prevention programs that have been promising in curbing substance-use trajectories.

In a recent Addiction Policy Forum webcast on cannabis, Sarah Vinson, M.D., professor and chair of psychiatry at Morehouse University School of Medicine, said, “We have been warning kids and their parents that cannabis is not a medicine for them. Cannabis use during adolescence and young adulthood may directly harm and compromise the developing brain. Research shows …one in six people who start using cannabis before the age of 18 can become addicted.”

All of the data on young people has been a reminder to rethink cannabis use in young people on the basis of clear risks.