Ask the Doctor: Is my teen using marijuana?

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Q: We heard there's a new study that says cannabis changes a teenager's brain. My wife and I suspect that at least one of our 16-year-old son's friends is getting high, and we worry about our son as well. Why isn't there more research about the health effects of cannabis?

A: Although a growing number of states are easing restrictions on cannabis, at this time it remains illegal under federal law. According to the Controlled Substances Act, cannabis is a Schedule l drug, along with heroin, LSD, methaqualone (Qualuude) and others. Drugs in this category are considered to have no accepted medical use and a high potential for abuse. As a result of its Schedule l status, studies about cannabis require a special license, which makes scientific research quite challenging.

A couple of years ago, the National Academies of Sciences, Engineering and Medicine published an analysis of cannabis studies completed over the last 20 years. The committee found evidence to support the use of cannabis to treat chronic pain and muscle spasms in people with multiple sclerosis, and to ease nausea and vomiting due to illness or chemotherapy. Among the risks of cannabis was an increase in traffic accidents when driving while high and a spike in accidental ingestion by young children in states where cannabis is legal.

The committee said it found evidence that cannabis use does not give rise to the same cancers that tobacco products do, but that respiratory function can suffer among cannabis smokers. Learning, memory and attention were found to be impaired after immediate cannabis use. Among the body's conclusions was a pressing need for regulatory changes to remove the numerous barriers to rigorous cannabis research.

When it comes to the study you're asking about, which was published in January in the Journal of Neuroscience, scientists at the University of Vermont reported that cannabis use affects the structure of the teenage brain. This held true even in teens who had used only small amounts of the drug a few times.

Specifically, researchers saw an increase in gray matter volume in the amygdala when compared to scans of brains of teens who had never used cannabis. The amygdala is the part of the brain involved in fear and other emotions. Changes to brain structure among the cannabis users were also noticed in the hippocampus, the part of the brain that plays a major role in learning and memory.

What these brain changes actually mean to the future development of the teens is not yet known. However, according to the analysis we discussed earlier, experimentation with substances of abuse, including cannabis, most often begins in adolescence and young adulthood. The committee also found evidence that starting to use cannabis at a younger age is linked to ongoing use that may become problematic.

A survey completed in 2017 found that 15 percent of kids between the ages of 12 and 17 are using cannabis. If you're worried that your son is among them, we think the best thing you can do is talk with him. Share the research, explain your concerns, and let your son know you want this to be the start of an ongoing dialogue.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.

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