Ask Dr. Pat

Dr. Pat Consults: “Is Marijuana as Harmless as My Son Says?”

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Dr. Patricia Yarberry Allen is a collaborative physician who writes a weekly “Medical Monday” column for Women’s Voices for Change. (Search our archives for her posts, calling on the expertise of medical specialists, on topics from angiography to vulvar melanoma.)

This week, Dr. Pat asks Megan Riddle, M.D., Ph.D., a psychiatry resident at the University of Washington and a graduate of the Weill Cornell/Rockefeller/Sloan-Kettering Tri-Institutional MD-PhD Program, for answers to a mother’s questions on marijuana’s effect on physical and mental health. Dr. Riddle is a member of Women’s Voices’ Medical Advisory Board.


Dear Dr. Pat:

Can you help settle an argument I am having with my son? He’s a sophomore in college and at school in Colorado, where it is legal to smoke marijuana, which is the crux of the issue. He says that marijuana is far safer than cigarettes or alcohol, with basically no health side effects. Is it really as harmless as he says? Although I admit that I tried it briefly when I was about his age, I worry about what sort of long-term effects it might have, and I want him to be informed.




Dr. Riddle Responds:

Dear Jane:

Now that marijuana is becoming legalized for both medicinal and recreational uses, your question is increasingly important.

Research has shown us that marijuana has an effect on both mental and physical health.

Marijuana’s Effects on Mental Health

First, despite what your son’s friends may be saying, marijuana is actually addictive. About 9 percent of those who try it become addicted, and the risk increases considerably for those who start experimenting during adolescence and those who smoke regularly. Indeed, 25 to 50 percent of daily smokers develop addiction with withdrawal symptoms that make it harder to quit.

Smoking during adolescence and early adulthood can have a significant impact on brain development. Neuroimaging studies that look at connections in the brain show that smoking marijuana affects regions that are critical for alertness, learning, and memory. Since the brain continues to develop until at least 21 years of age, your son is still actively laying down connections that can be affected by his marijuana use. This may be part of the reason why frequent marijuana use in adolescence is linked to lower IQs in adulthood. Also, although many recognize that they are mentally slower while acutely intoxicated, they may not realize that studies have shown that a certain degree of slowing continues for days after use, which can have a significant effect on performance.

Your son claims that marijuana is “safer than alcohol.” Note that while we’ve all been taught not to drink and drive, many don’t realize the dangers of smoking marijuana and driving. Smoking even a fairly small amount doubles one’s risk for a traffic accident; at higher levels of use, the rate increases to 3 to 7 times, similar to the effects of alcohol.

Marijuana use is associated with a number of mental health issues. For those already at risk of developing a psychotic disorder like schizophrenia–such as having a close relative with the disorder–marijuana use is associated with increased likelihood of developing a psychotic disorder and an earlier onset of symptoms. Some studies have suggested that there is an increased rate of anxiety and depression amongst users. It is unclear, however, whether the drug use leads to the mental illness or is a result of the “self-treating” for the illness—or neither.  

Your son is right in some ways–evidence suggests that marijuana is safer than cigarettes with regard to lung cancer, although studies have been somewhat mixed. Interestingly, marijuana actually contains about three times the tar found in cigarettes and 50 percent more carcinogens (cancer-causing agents). However, people tend to smoke far fewer joints than cigarettes, which may be why we don’t see increased rates of lung cancer. Still, frequent marijuana smokers do appear to have more respiratory infections than non-smokers, as well as worsening of underlying lung problems like asthma or cystic fibrosis.

Marijuana’s Effects on Physical Health

In rare instances, marijuana use has been associated with increased risk for heart problems, including heart attack, even in young individuals.

And here’s a fact that will be of particular interest to men: marijuana decreases testosterone levels. This can lead to decreased libido and impotence.

Because of its impact on various hormones, marijuana use can also cause breast growth in men. For women, excessive use can lead to milk production even when the woman is not pregnant or nursing.

While you are right to be concerned about the long-term effects marijuana can have on your son’s health, a key question to be asking now is this: What role does marijuana use have in your son’s life? Some people use occasionally, smoking a joint on the weekend with friends while continuing to have an engaging and productive life. For many, this can be a phase—marijuana use peaks in individuals around your son’s age. Such occasional recreational use is less concerning than that of the individual who smokes alone and uses marijuana to cope with difficult emotions. If your son finds his thoughts shifting from friends and school to fixating on when he can smoke his next joint or make his next purchase, there is more cause for concern, since he may be on the way to developing addiction. If he feels that the marijuana is taking up more of his life than is healthy, I would encourage him to seek assistance at his college’s student health center or with his primary care doctor.

I want to applaud you for having these difficult conversations with your son. While you are right that your ability to control your son’s behavior is limited at best, being able to discuss these issues in a calm, nonjudgmental way keeps the channels of communication open on an important topic.

Dr. Megan Riddle



Jouanjus, E., Lapeyre-Mestre, M., Micallef, J., French Association of the Regional, A., & Dependence Monitoring Centres Working Group on Cannabis, C. (2014). Cannabis use: signal of increasing risk of serious cardiovascular disorders. J Am Heart Assoc, 3(2), e000638.

Marijuana Anonymous. (2014). The Twelve Questions of Marijuana Anonymous.

Saad, L. (2013). In U.S., 38% Have Tried Marijuana, Little Changed Since ’80s. Gallup.

Teitelbaum, S. A., DuPont, R. L., & Baily, J. A. (2014). Cannabis use disorder: Treatment, prognosis, and long-term medical effects. In A. J. Saxon (Ed.), on the site UpToDate,

Volkow, N. D., Compton, W. M., & Weiss, S. R. (2014). Adverse health effects of marijuana use. N Engl J Med, 371(9), 879.


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