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What 10,000 studies say about the medical benefits — and risks — of weed

Smoking weed probably won’t give you cancer, but it might cause lung problems, contribute to mental health issues, and affect your memory. It can also be used to treat chronic pain and a broad range of other medical conditions, but a lot more research is still needed to determine whether it’s truly safe and effective.

Those are the key takeaways from a landmark report published Thursday by the National Academies of Sciences, Engineering, and Medicine. The federal advisory panel didn’t conduct any new research, instead analyzing the findings of more than 10,000 previous scientific studies on marijuana and the plant’s derivatives published since 1999.


“The lack of any aggregated knowledge of cannabis-related health effects has led to uncertainty about what, if any, are the harms or benefits from its use,” said Marie McCormick, a Harvard pediatrician who chaired the committee that published the report. “We conducted an in-depth and broad review of the most recent research to establish firmly what the science says and to highlight areas that still need further examination.”

Key findings from the report include:

Marijuana seems to work for chronic pain.
“Patients who were treated with cannabis or cannabinoids were more likely to experience a significant reduction in pain symptoms,” the researchers wrote.

You shouldn’t drive stoned.
“Evidence suggests that cannabis use prior to driving increases the risk of being involved in a motor vehicle accident,” the study found.

Smoking weed doesn’t appear to cause lung cancer.
The researchers found “evidence that suggests smoking cannabis does not increase the risk for cancers often associated with tobacco use.” But they also noted that regular use of weed “is associated with more frequent chronic bronchitis episodes and worse respiratory symptoms.” The good news, however, is that those symptoms seem to go away when people quit smoking.

Mental health problems are a possibility.
The theory that pot smoking is linked to schizophrenia has been around for years, but many respected researchers believe it only leads to earlier onset in people already predisposed to the illness. That said, the new study found that “cannabis use is likely to increase the risk of developing schizophrenia, other psychoses, and social anxiety disorders, and to a lesser extent depression.”

Government red tape is impeding important research.
While 29 states and Washington, D.C., now allow some form of medical marijuana, science is still struggling to catch up with the drug’s prevalence. The new study found “substantial evidence” that marijuana products work for multiple sclerosis–related muscle spasms, and “conclusive evidence” that weed can effectively treat “chemotherapy-induced nausea and vomiting,” but “specific regulatory barriers, including the classification of cannabis as a Schedule I substance, impede the advancement of research.”

You can read the National Academies of Sciences, Engineering, and Medicine’s own summary of the study here.