Marijuana Could Cause Brain Damage in Teenagers, Doctors Warn

Marijuana use may not be completely without its risks. ROBYN BECK/AFP/Getty Images

This month California is on track to legalize the use of marijuana for adults aged 21 and older, but last week state health officials issued a public warning that the drug may still be dangerous for underage users. According to the official warnings, evidence suggests the drug could damage still developing brains, and therefore should not be used by minors.

As of January 1, 2018, adults aged over 21 can legally possess up to an ounce (28 grams) of marijuana and are allowed to keep and grow up to six marijuana plants at home, The BBC reported. However, in the wake of the new law, San Francisco health director Barbara Garcia emphasized that using marijuana is not only still illegal for minors it is also potentially dangerous.

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"Using cannabis is not something that every teenager does, despite the myths and messages to the contrary," Garcia said, KRON reported. "We'd like to keep it that way and support youth in their decision-making. We want to make sure they know that cannabis is still illegal if you're under 21."

Garcia urged young adults to resist targeted advertising towards them and abstain from the drug until they are of legal age to use it in their state.

"Delaying cannabis consumption is the smart thing you can do for your brain, which is still developing into your 20s," San Francisco Health Officer Dr. Tomas Aragon told KRON.

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The warning does have scientific backing. Although researchers are still not clear on the exact effects of marijuana use, mounting evidence does suggest the drug may affect younger brains differently than older brains. While the science is still not definitive, it is clear that individuals who use marijuana during adolescence are more likely to develop a substance dependency, schizophrenia and have a lower IQ later in life than individuals who abstain from the drug until they are older.

The reason for these associations is not entirely clear, but other research has shown that heavy marijuana use for long periods of time can change connections in brain structure and significantly lower grey matter volume. However, it's not clear if these brain changes are only in individuals who started using during adolescence, or if these changes are related to any real life behavior differences.

One hypothesis suggests that THC, the main psychoactive drug in marijuana, affects and alters the endocannabinoid system in teens. This system controls a number of important behaviors such as neurodevelopment, stress response and emotions, The American Psychological Association reported. Researchers already note that this system responds to THC, but in young adults it is still forming so its response to THC could be more disruptive.

Despite some scientific uncertainty, many doctors and researchers agree that enough evidence exists to suggest that teens should abstain from the drug until later in life.

"There are a lot of open questions" about the long-term effects of marijuana, said Susan Weiss, Ph.D., director of the division of extramural research at the National Institute on Drug Abuse, the American Psychological Association reported. "But there's a growing literature, and it's all pointing in the same direction: Starting young and using frequently may disrupt brain development."