How does cannabis affect the body?
Experts say regular cannabis users are at higher risk for a host of negative health impacts, from depression to heart disease.
In recent years, 24 states and the District of Columbia have legalized recreational cannabis. This changing landscape has led to a dramatic rise in marijuana consumption, with some 62 million Americans using the drug. But legalization doesn’t mean that regular consumption is completely safe.
A growing body of evidence has documented an array of concerning marijuana health effects beyond just dry mouth and fatigue and includes both mental and physical illnesses. One study even links cannabis consumption to heart disease.
“People think about Bob Marley when they think about cannabis. They think it’s natural, it’s Mother Nature, that it’s not going to do any harm,” says Marco Solmi, a psychiatrist at the University of Ottawa. Yet his review of the substance published in the BMJ found numerous potential problems.
Cannabis isn’t dangerous in the same way opioids are, says Deborah Hasin, an epidemiologist at Columbia University who has researched cannabis use and abuse. “People don’t die from cannabis overdose,” she says. “But it can have a lot of other consequences to both physical and psychological health.”
Stronger cannabis strains
Some of the problems can be attributed to the stronger strains now available. Today’s products are “not your grandmother’s weed,” as Maria Rahmandar, medical director of the substance use and prevention program at Chicago’s Lurie Children’s Hospital, put it at a recent discussion of cannabis at the National Academies of Sciences, Engineering, and Medicine.
“These products are much more potent and come in so many different formulations, that it’s very different from those in the sixties and even the nineties,” Rahmandar says.
The way people consume cannabis today increases the amount of the active ingredient, tetrahydrocannabinol (THC), they ingest. Vaping and edibles generally deliver high doses compared to rolling and smoking joints, Rahmandar says.
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How cannabis affects the brain
One of the lesser known but troublesome risks of regular cannabis use is substance-abuse psychosis, where a person has delusions or paranoia, hears voices, and otherwise temporarily loses touch with reality. The substance use disorder is a short-term side effect, generally resolving within a few days. But some cases require hospitalization.
This condition can occur with any psychologically altering substances, but there’s increase risk from cannabis even compared to cocaine, Solmi says.
“You’re more likely to develop substance-abuse psychosis if you use cannabis daily, but I cannot tell you there’s a safe amount that would prevent this,” he says. Young adults and males are the most prone.
Especially worrisome, up to a third of people who experience substance-abuse psychosis go on to develop the more permanent condition of schizophrenia, Solmi says.
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Observational studies also connect other mental health conditions to frequent cannabis use. Solmi’s review found that depression increases, as does violence among dating couples.
And since cannabis causes cognitive impairment—as well as visual impairment—car accidents have risen in recent years among users who drive while under the influence.
Experts especially worry about the long-term effects for teenagers’ mental health. Some 17 percent of tenth graders report using cannabis, even though no state has legalized the drug for anyone under 21.
Adolescents are 37 percent more likely to develop depression by young adulthood if they regularly use cannabis compared to non-users. Rates of suicide are also higher.
“Teenage brains are going through a time of maturity and pruning, so when substances are put in there, they have more of an influence than they do on adult brains,” Rahmandar says.
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Cannabis and heart disease
Regular use of marijuana can also lead to significant physical problems.
People who use the drug regularly have a higher risk for heart attack, stroke, and other heart disease, according to a large population-based study published in the Journal of the American Heart Association. Heart attack rates rose 25 percent while stroke increased 42 percent in this group, the researchers found.
This likely occurs because THC affects blood flow in the arteries and because receptors for cannabinoids exist throughout the cardiovascular system, the authors state. People who smoke their weed also boost their heart disease risk from the particulate matter they inhale alongside the THC.
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Other studies have linked cannabis with improving nausea and vomiting after chemotherapy. However, the BMJ review found regular users can actually suffer from an extended vomiting condition known as cannabinoid hyperemesis syndrome. “This is rare, but it’s increasing as more people use the drug,” Hasin says.
Pregnant women who use cannabis regularly are more likely to have preterm births and dangerously small babies. More research is needed to determine whether this results from the drug itself or from other lifestyle factors among those who choose to use cannabis while they are pregnant, Solmi says.
Cannabis addiction is a real concern
Many people perceive cannabis to be safer than alcohol, but one in five cannabis users develop an addiction to the drug. Symptoms of cannabis drug use disorder are like those for other substances.
“If people experience cravings, feel they need more and more to get the same effects, they’ve had unsuccessful attempts to quit or cut down,” or have any of several other symptoms “that’s a warning,” Hasin says.
As with alcohol, marijuana addiction can lead to many problems, including personal, financial, legal, and health issues.
Certain groups are at particularly heightened risk for this addiction. Rates in veterans have increased substantially since 2005, Hasin found in her research.
She attributes this to a combination of increased potency and greater acceptance of the drug from its legal status, as well as the likely use of weed to self-medicate chronic pain and psychiatric disorders.
“The [Veterans Affairs] has done a good job of reducing unnecessary prescribing of opioids in veterans, so some of them might be turning to cannabis,” she says.
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Young people are also at risk for developing this disorder. Youth who begin using the drug at earlier ages or who have a family history of addiction especially increase their odds for trouble.
“People younger than 25 should avoid cannabis altogether,” Solmi says. “They have no idea how they will react to cannabis. You’re gambling with your brain and your health.”
For everyone else, moderation is key.
“This isn’t a benign substance that has no risk,” Rahmandar says. “Most users will be fine, but we can’t predict who will develop problems” from regular cannabis use.
