Skip to content

Marijuana Can Cause This Scary Side Effect, Study Suggests

Serious cannabis side effects, according to doctors.
FACT CHECKED BY Emilia Paluszek

The research into the safety and efficacy of marijuana is ongoing—but doctors are warning of some very alarming side effects related to cannabis use. "As I frequently tell patients, if you read the warning labels of any medications that are commonly prescribed, each and every one has potential side effects, some serious," says Peter Grinspoon, MD. "There is truly no free lunch with medication, including medical cannabis; however, with good education and with legal regulation (which leads to a safer product), many of the above harms can be avoided or minimized." Here are five side effects of marijuana to be aware of. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Permanent Brain Change

Doctor examines MRI scan of head, neck and brain of patient

Growing evidence shows that cannabis use could change the brains of teenagers who use marijuana, even occasionally. "Most people would likely assume that one or two uses (joints) would have no impact, so we were curious to study this — and especially to investigate if first uses may actually produce brain changes that affect future behavior like subsequent use," says Hugh Garavan, professor of psychiatry at the University of Vermont School of Medicine. "At the age at which we studied these kids (age 14), cortical regions are going through a process of thinning. So, one possibility is that the cannabis use has disrupted this pruning process, resulting in larger volumes (i.e., a disruption of typical maturation) in the cannabis users. Another possibility is that the cannabis use has led to a growth in neurons and in the connections between them."


Erectile Dysfunction

Sad man sitting on a bed, girlfriend in the background.

Research shows men who use marijuana are twice as likely to experience erectile dysfunction (ED) compared to those who don't use any. "Understanding emerging risk factors for ED, particularly in relation to the increasing legalization of cannabis, is highly important," says Damiano Pizzol, MD, Ph.D. "Approximately 147 million people — 2.5% of the world's population — consumes cannabis annually. Although no medical specialty is dedicated to monitoring cannabis use and abuse, we believe urologists should make all male patients aware of the associated risk of ED."


Personality Changes

Offended woman sitting back to lover looking away avoiding talking

Regular use of marijuana could lead to negative personality changes, doctors warn. "Research shows that brain abnormalities are linked with chronic pot smoking," says Carrie Barron, M.D. "Scientists from Harvard and Northwestern observed an altered amygdala and nucleus accumbens (associated with fear, aggression, paranoia, and addiction) in study participants. While more research needs to be done, evidence suggests that those who smoke regularly may be at risk."


Heart and Lung Issues

There is evidence showing cannabis can have a dangerous impact on heart health and heart conditions. "People who use cannabis need to know there are potentially serious health risks in smoking or vaping it, just like tobacco smoke," says Rose Marie Robertson, M.D., FAHA, the deputy chief science and medical officer for the American Heart Association and co-director of the AHA Tobacco Center for Regulatory Science. "The American Heart Association recommends  that people not smoke or vape any substance, including cannabis products, because of the potential harm to the heart, lungs and blood vessels."


Stroke Complications

Stressed woman drying sweat using a wipe in a warm summer day in a park

Cannabis use can lead to complications related to stroke, experts say. "We're all vulnerable to a bleeding stroke or a ruptured aneurysm, however, if you're a routine marijuana user, you may be predisposed to a worse outcome from a stroke after the rupture of that aneurysm," says Michael T. Lawton, M.D. "When people come in with ruptured aneurysms, and they have a history of cannabis use or are positive on a toxicology screen, it should raise a red flag to the treating team that they are at higher risk of vasospasm and ischemic complication. Of all the substances detected in the toxicology screen, only cannabis raised the risk of delayed cerebral ischemia."

Ferozan Mast
Ferozan Mast is a science, health and wellness writer with a passion for making science and research-backed information accessible to a general audience. Read more about Ferozan
Filed Under