Here’s What Experts Know About How Marijuana Affects Your Body

A comprehensive 440-page report seeks to dispel fact from fiction

By Christa Sgobba

Currently, 28 states and the District of Columbia have legalized medical marijuana, and eight of those states plus D.C. allow pot for recreational use, too. The legal landscape is changing, but lots of questions still remain regarding marijuana on the health front.

Now, a new report seeks to clarify the health effects of pot. Published by the National Academies of Sciences, Engineering, and Medicine, this comprehensive, rigorous report reviews the evidence of scientific research published on marijuana since 1999—and makes some important conclusions.

First, the researchers reviewed the evidence on marijuana’s therapeutic effects for health conditions. The takeaway? There’s conclusive evidence to show cannabis or cannabinoids is effective for treatment of chronic pain, helping chemotherapy-induced nausea and vomiting, and improving spasticity symptoms with multiple sclerosis.

On the other hand, there’s no evidence, or insufficient evidence, to show that pot can help treat cancers, irritable bowel syndrome, epilepsy, symptoms of ALS, or motor symptoms in Parkinson’s disease.

When looking at incidence of cancer, the researchers concluded there’s moderate evidence showing no link between marijuana use and lung cancer or head and neck cancers. And there’s insufficient evidence to support a link either for or against pot and incidence of esophageal, prostate, and bladder cancers. (Find out if you should get the PSA test to screen for prostate cancer.)

As for other health outcomes, the researchers determined that there’s substantial evidence that pot use worsens respiratory symptoms and causes more frequent episodes of bronchitis. But there’s no evidence that marijuana increases your risk of heart attack—and no or insufficient evidence that it increases your chances of dying prematurely.

Still, evidence supports the fact that pot use can hurt you in other ways. There’s substantial evidence showing that marijuana increases your risk of car accidents, and moderate evidence that it can lead to cognitive impairments in learning, memory, and attention. (Here’s what you need to know if you’re traveling to smoke legal marijuana.)

While the comprehensive review of the available evidence does give us a better understanding of what marijuana really does to your body, there’s a lot we still need to learn. More research—comprised of high-quality, controlled trials and observational studies—still needs to be done, the researchers say.