What we know—and what we don’t—about marijuana’s health effects

May 4, 2026

5 min read

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What we know—and what we don’t—about marijuana’s health effects

Marijuana is far from a “silver bullet” for various illnesses, but it has some promising applications, scientists say

By Jackie Flynn Mogensen edited by Claire Cameron

Victoria Bee Photography/Getty Images

Medical marijuana could finally be inching toward federal approval. After decades of advocacy from cannabis proponents and the marijuana industry, the Trump administration is moving to ease some cannabis restrictions and boost research on the drug’s therapeutic uses. Most U.S. states—40 in all—and the Washington, D.C., already allow medical marijuana as a treatment for dozens of conditions, from arthritis to inflammatory bowel disease, hepatitis C, cancer, glaucoma, Alzheimer’s, and more. But despite cannabis’s popularity, experts say that the scientific evidence as to whether it can actually treat many of these health issues is often thin—though promising.

“Some people will have you believe that it can help every condition,” says Jack Wilson, a postdoctoral research fellow at the Matilda Center for Research in Mental Health and Substance Use at the University of Sydney in Australia. “They think that it’s some sort of silver bullet, but that’s just not the case.”

Cannabis is inherently difficult to study. The plant, Cannabis sativa, contains hundreds of compounds, including more than 100 cannabinoids—and each of these may have their own potential health effects. Furthermore, people take cannabis in myriad different forms—flowers, waxes, edibles, tinctures, creams, suppositories, and more—and at varying doses. It has also been highly controlled on the federal level, where cannabis has been broadly considered to be in the same class of drugs as heroin and LSD. And that has made research hard to do and expensive because it has required labs to get extra federal permissions and to invest in extra layers of security.

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There is also a dearth of clinical evidence. Most of the available medical marijuana products on the market have not been tested in large-scale clinical trials—the gold standard for determining whether a treatment or intervention is safe and effective. “That’s why there’s so much confusion,” says Ryan Vandrey, a professor of psychiatry and behavioral sciences at Johns Hopkins University. “That’s why there’s such a lack of good clinical evidence.”

That’s not stopping people from using marijuana as medicine, however. “Societally, people are moving on with this as a medicine with very little data,” says Margaret Haney, director of the Cannabis Research Laboratory at Columbia University. “People say, ‘Talk to your doctor.’ Well, your doctors don’t know anything because they don't have the data.”

Scientific American spoke with several cannabis researchers to learn what potential medical marijuana treatments are backed by science, what areas of research are most promising and how a possible shift in federal regulations could help close some of the evidence gaps.

What does cannabis do to our body?

Smoking, vaping, eating or otherwise consuming cannabis can have various effects on the brain and body. Some of the most common include relaxation, as well as adverse reactions such as heightened anxiety or paranoia.

The psychoactive effect of cannabis largely arises from the cannabinoid tetrahydrocannabinol (THC), which binds to the so-called endocannabinoid system, a network of neural circuits throughout the body that help regulate things such as sleep, mood and brain function. Cannabinol (CBD), another commonly consumed cannabinoid, interacts with the endocannabinoid system, too, but in a less noticeable way.

How much of a cannabis product a person ingests, what their age and individual physiology are, what form of cannabinoids are in the drug and how they take it can all influence its effects. For instance, if a person inhales a cannabis product, they might feel the physiological effects within a few minutes, says Igor Grant, a distinguished psychiatry professor at the University of California, San Diego. But consuming cannabis in an edible—thus sending it through the gastrointestinal tract—may mean the effects will take longer to feel.

What uses of medical marijuana are best supported by evidence?

Cannabis has been used as a medical therapeutic since ancient times, with records of its use dating back to at least 2800 B.C.E. in China. Today in the U.S., however, very