Do marijuana's benefits outweigh its risks? Here's a look at the pros and cons of the drug.

By Amanda MacMillan
Updated: March 29, 2019

As more states legalize marijuana, it's important to know the pros and cons of pot—and what exactly it might do for your health.

Health looked at recent research and spoke with several experts about who might want to try it, who should avoid it, and what any marijuana user should know.

It may help with anxiety and PTSD

The relaxing effects of marijuana are well known, so it’s not surprising that a 2016 paper in the journal Clinical Psychology Review concluded that it may have benefits for people with depression, social anxiety, and post-traumatic stress disorder. A study published in Drug and Alcohol Dependence also found that a very low dose of THC, one of the main compounds in marijuana, helped people feel less nervous about a public-speaking task.

But it may not be that simple: That dose was equivalent to only a few puffs on a marijuana cigarette, say the study authors. They also found that slightly higher amounts of TCH—anything that would produce even a mild high—actually made anxiety worse. Other research has also suggested that marijuana may be more harmful than helpful for people with certain mental health conditions, like psychosis or bipolar disorder.

The research “indicates cannabinoids could be helpful for people with anxiety,” lead author Emma Childs, PhD, associate professor of psychiatry at the University of Illinois at Chicago, tells Health. But more research is needed, she says, to determine appropriate dosages and delivery methods, and to prevent the opposite effects from happening.

It can relieve chronic pain and nausea

Pain relief is a common use for medical marijuana, and the National Academies of Sciences concluded there is indeed good evidence to support this practice. Marijuana products also appear to be effective at calming muscle spasms caused by multiple sclerosis and easing nausea and vomiting due to chemotherapy, the report stated.

The National Academies also determined that there is moderate evidence that cannabis or cannabis-derived products may help people who have trouble sleeping due to sleep apnea, fibromyalgia, or chronic pain.

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People with epilepsy may benefit—even kids

In a New England Journal of Medicine study, cannabidiol oil—a derivative of marijuana—reduced seizures by 39% in children with Dravet syndrome, a rare form of epilepsy. That was big news for parents who have been using medical marijuana for years, often illegally, to help their kids suffering from this debilitating condition.

The cannabidiol oil used in the study—approved by the FDA in 2018 and marketed as Epidiolex—won’t make people high, because it doesn’t contain THC. Experts say that results may be riskier and more unpredictable with other marijuana products.

It may be a safer alternative to opioids

Despite beliefs that marijuana is a “gateway drug,” research suggests that the use of medical marijuana may actually reduce dependence on dangerous prescription painkillers like those fueling the nation’s opioid epidemic.

In a 2016 study in the journal Health Affairs, researchers found that there were 1,826 fewer daily doses of painkillers prescribed per year, on average, in states where medical marijuana was legal compared to states it’s not. And in a review article published in Trends in Neuroscience, researchers wrote that cannabinoids may help people recover from opioid addiction. Human trials have been limited because of marijuana’s classification as a Schedule 1 drug—but the authors argue that more studies are urgently needed.

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It may have anti-cancer effects, but research is limited

Olivia Newton John uses cannabiodiol oil (along with conventional medicine) to fight her metastatic breast cancer, the actress’s daughter recently revealed. Studies have shown that the oil may inhibit the growth of cancer cells outside of the human body, but there haven’t been any real-life trials to back up these findings.

Gregory Gerdeman, PhD, assistant professor of biology at Eckerd College, told Time that there have also been anecdotal patient reports and “increasing numbers of legitimate clinical case studies … that all indicate tumor-fighting activities of cannabinoids.” It’s still unknown, however, whether traditional forms of marijuana would be an effective cancer therapy, or what cancer types it might actually work against.

Parents (and expectant parents) should know the risks

As pot use becomes more prevalent, more pregnant women are getting high, according to a 2016 JAMA study—either for recreational use or, sometimes, to treat morning sickness. But evidence suggests that prenatal exposure to marijuana is associated with developmental and health problems in children, including low birth weight, anemia, and impaired impulse control, memory, and attention, the authors wrote. Until more is known for sure, they say women who are pregnant or considering becoming pregnant should be “advised to avoid using marijuana or other cannabinoids.”

Current parents should also use marijuana with caution, University of Washington researchers suggest. Their study in Prevention Science found that people tend to cut back on marijuana use once they have kids, but they don’t always quit. That’s concerning, says lead author and research scientist Marina Epstien, PhD, because parental marijuana use is strongly related to children’s use—and children’s use is associated with higher rates of health problems.

“Children watch what their parents do,” Epstein tells Health. “I would encourage parents to be talking to their kids and be clear about expectations for their kids about using or not using marijuana and the amount, especially with their teenagers.”

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Heart problems could make it extra risky

In 2014, a study in Forensic Science International documented what German researchers claimed to be the first known deaths directly attributed by intoxication from marijuana. The authors pointed out that, during autopsies, it was discovered that one of the two young men had a serious but undetected heart problem, and that the other had a history of drug and alcohol use.

The researchers concluded that the absolute risk of cannabis-related cardiovascular effects is low, especially for healthy people. But they say that people who are at high risk for heart-related complications should avoid the use of cannabis, since it can have temporary effects on the cardiovascular system.

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It’s not safe to use marijuana and drive

A study by the Insurance Institute for Highway Safety found that insurance claim rates for motor vehicle accidents from 2012 to 2016 were about 3% higher in states with legalized marijuana than in states without. But other studies have found no such increase in fatal car crashes in states with legalized marijuana, compared to similar states without.

Experts say it’s possible that driving under the influence of marijuana may increase the risk of minor fender benders—but may also reduce rates of alcohol consumption and therefore help prevent more serious, deadly crashes. The bottom line? Driving while stoned may be less dangerous than driving drunk, but it’s still riskier than driving sober.

Weed smoke is still smoke—and still has health risks

The Canadian Research Initiative in Substance Misuse published a set of “lower-risk cannabis use guidelines,” aimed at helping people who use marijuana make responsible decisions about their health. (The drug was legalized for recreational use in Canada in 2018.) Among other advice, the guidelines urge people to “avoid smoking burnt cannabis,” which can harm the lungs and respiratory system—especially when combined with tobacco.

They recommend choosing vaporizers or edibles instead, but caution that these methods also come with some risks. And if you do smoke cannabis, the guidelines say, “avoid ‘deep inhalation’ or ‘breath-holding,’” which increase the amount of toxic materials absorbed by the body.

It’s not just lung-health that frequent weed smokers should worry about, either. A study in the Journal of Periodontology found that frequent marijuana users were twice as likely as people who didn’t use frequently to have gum disease, even after controlling for other factors such as cigarette smoke. The research didn’t distinguish between methods of marijuana use, but they do point out that smoking is the most common form of recreational use.

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For recreational users, less is safer

Canada’s low-risk guidelines may sum it up best with this statement: “To avoid all risks, do not use cannabis. If you decide to use, you could experience immediate, as well as long-term risks to your health and well-being.” The guidelines also recommend avoiding marijuana use during adolescence, because the later in life people start using the drug, the less likely they are to experience these problems.

Finally, the guidelines recommend adults choose natural cannabis over dangerous synthetic versions, and limit themselves to “occasional use, such as on weekends or one day a week at most.”

Some marijuana users develop a condition called cannabinoid hyperemesis syndrome

Cannabinoid hyperemesis syndrome (CHS) causes some marijuana users to experience severe nausea, vomiting, and abdominal pain. A study published in the Annals of Internal Medicine found that, among study participants, 18.4% of people who inhaled cannabis and ended up in the emergency room of a Colorado hospital and 8.4% of those who ate edible cannabis and ended up in the emergency room had CHS symptoms.

CHS hasn’t been studied extensively, says Joseph Habboushe, MD, who specializes in emergency medicine at NYU Langone. While it’s possible to use marijuana for years without experiencing symptoms of CHS, once a person does experience CHS symptoms, the symptoms tend to stick around as long as the person continues using marijuana. Stopping marijuana use is the only known way to permanently alleviate CHS symptoms, but it takes time. “We know that if you stop smoking you get better, but it takes days to weeks,” Dr. Habboushe says.

This post was originally published on June 29, 2017 and has been updated for accuracy.