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

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.