Article by Aaron E. Carroll, New York Times
The benefits and harms of medical marijuana can be debated, but more states are legalizing pot, even for recreational use. A new evaluation of marijuana’s risks is overdue.
Last year, the National Academies of Sciences, Medicine and Engineering released a comprehensive report on cannabis use. At almost 400 pages long, it reviewed both potential benefits and harms. Let’s focus on the harms.
The greatest concern with tobacco smoking is cancer, so it’s reasonable to start there with pot smoking. A 2005 systematic review in the International Journal of Cancer pooled the results of six case-control studies. No association was found between smoking marijuana and lung cancer. Another 2015 systematic review pooled nine case-control studies and could find no link to head and neck cancers.
Another meta-analysis of three case-control studies of testicular cancer found a statistically significant link between heavier pot smoking and one type of testicular cancer. But this evidence was judged to be “limited” because of limitations in the research (all of which was from the 1990s).
There’s no evidence, or not enough to say, of a link between pot use and esophageal cancer, prostate cancer, cervical cancer, non-Hodgkin’s lymphoma, penile cancer or bladder cancer. There’s also no evidence, or not enough to say, that pot has any effect on sperm or eggs that could increase the risk of cancer in any children of pot smokers. (Using marijuana while pregnant does pose other risks, as discussed below.)
Another major risk with cigarettes, heart disease, isn’t clearly seen with pot smoking. Only two studies quantified the risk between marijuana use and heart attacks. One found no relationship at all, and the other found that pot smoking may be a trigger for a heart attack in the hour after smoking. But this finding was based on nine patients, and may not be generalizable.