Study links adolescent cannabis use to later mental health diagnoses

A new longitudinal study finds that cannabis use among adolescents increases risks of being diagnosed with bipolar and psychotic disorders, as well as anxiety and depression, years later. Researchers analyzed health data on 460,000 teenagers in the Kaiser Permanente Health System in Northern California and followed the teens until they were 25 years old.

The data included annual screenings for substance use and any mental health diagnoses from the health records. Researchers excluded adolescents who had symptoms of mental illnesses before using cannabis. They found that teens who reported using cannabis in the past year were at a higher risk of being diagnosed with several mental health conditions a few years later, compared to teens who did not use cannabis.

Teens who reported using cannabis had twice the risk of developing two serious mental illnesses: bipolar and psychotic disorders. Only a small fraction — nearly 4,000 — of all teens in the study were diagnosed with each of these two disorders.

The study also found that the risk for more common conditions like depression and anxiety was higher among cannabis users. Depression alone went up by about a third, and anxiety went up by about a quarter. The link between cannabis use and depression and anxiety got weaker for teens who were older when they used cannabis.

As more lawmakers move to legalize and decriminalize possession and use of marijuana, more medical researchers are diving into learning more about how the drug affects the human body. Among health experts, the jury is still out on THC, CBD and the use of marijuana in general, as those in medical and research fields weigh the benefits and risks.

In plain terms, THC is the part of cannabis that gets you high. A 2023 meta-analysis of studies on cannabis's impact on health concluded that it can be beneficial in managing pain for people with several health conditions, but not without side effects. Experts as a whole say more research is needed to give a conclusive answer about benefits and risks.

Health experts hesitated to label one THC product as the safest because there still is not much research on its health effects, especially long-term health effects. Sticking to products with a lower concentration of THC, or consuming smaller amounts of THC in general, is relatively less risky.

Each form of marijuana consumption offers pros and cons when it comes to dosing versus exposure to dangerous compounds. Smoking a joint may allow someone to pace themselves more effectively because the high comes along faster than other forms, but inhaling combusted marijuana is very damaging. Edibles eliminate the dangers of inhaling combustion by-products, but the fact that they are metabolized much more slowly makes it more difficult to self-regulate dosage. Concentrates, which are typically consumed via vaping, are likely the most dangerous option because they contain very high levels of THC.

More research is needed, but it appears high concentrations of THC can increase the likelihood of developing addiction, as well as experiencing side effects such as anxiety, agitation, paranoia and psychosis. Research supports the idea that young people and those who are pregnant are among the populations who should avoid cannabis as a whole because of high risks and harms.