It's no surprise that Americans are smoking up a storm. Medical marijuana is now legal in more states than it's not. But nationwide, men seem to be the ones taking the most advantage of the country's softening views on weed—and the verdict is still out on what that means for the health of their brains.
A recent study from Columbia University's Mailman School of Public Health found that while the number of pot smokers is on the rise among both men and women, the rate of increase has been higher for guys. Between 2002 and 2014, an additional 6 million men and 4 million women picked up the habit—with most of the spike coming after the 2007 recession. When the researchers narrowed in on low-income groups, the gender gap become more vast: In households earning less than $20,000 a year, marijuana use jumped 6 percent for men and only 2 percent for women.
A drug-use gender gap would be noteworthy under any circumstances, but another recent study suggests there could be reason to worry: Research in the Journal of Alzheimer's Disease raises the possibility that marijuana users have less blood flow to their brains, even in key areas like the hippocampus.
"The hippocampus is the core of memory formation in the brain," says study author Lantie Elisabeth Jorandby. "If this area is not working well, has low blood flow, and is damaged, this will prevent people from maintaining or making new memories, a hallmark of Alzheimer's disease."
The researchers aren't saying that weed causes Alzheimer's, but the correlation is hard to ignore. It could also be that marijuana worsened problems that already existed from genetics, poor diet, physical trauma, or infection. "With brains that are already vulnerable, adding something like marijuana could be akin to throwing gasoline on a fire," says Jorandby.
One obvious vulnerability could be inherent in the group studied: All of the participants in the blood-flow brain study had been previously diagnosed with a marijuana use disorder, says Gary L. Wenk, a marijuana researcher and director of the neuroscience undergraduate programs at Ohio State University. "That means that these people were true addicts, not your normal weekend smoker." And previous addictions from alcohol, nicotine, or even extreme caffeine use could skew the sample.
So the study is being seen as just one more data point in our collective understanding of the safety of marijuana. In fact, some of Wenk's research indicates an opposite result—that low doses of pot may actually help prevent inflammation in the brain, an in turn, prevent Alzheimer's disease. That researchers are unable to get reliable, consistent results is no surprise given the tough regulations on marijuana testing. The federal government classifies the plant as a schedule 1 substance, meaning it has "no currently accepted medical use and a high potential for abuse." "Sadly, due to the FDA scheduling of marijuana, we have no solid evidence regarding the benefits of marijuana in humans," says Wenk. What we have instead are small observational studies like the ones mentioned here, which waffle in their results.
Women are currently more likely to develop Alzheimer's disease, but if the results of the two recent studies are to be trusted, men—and particularly those living closest to poverty—may see their numbers rising. So while researchers fight the red tape to study the true, long-lasting effects of cannabis' effect on health, it's best to keep your smoking in moderation. Wenk notes: "High doses of any drug or nutrient are probably bad for the brain."