MJ: The good, bad and unknown

A report by the National Academies of Sciences, Engineering and Medicine lists nearly 100 conclusions about marijuana and its similarly acting chemical cousins, drawing on studies published since 1999. Committee members cautioned that most conclusions are based on statistical links between use and health, rather than direct demonstrations of cause and effect.

The review found strong evidence that marijuana can treat chronic pain in adults and that similar compounds ease nausea from chemotherapy, with varying degrees of evidence for treating muscle stiffness and spasms in multiple sclerosis.

Limited evidence says marijuana or the other compounds can boost appetite in people with HIV or AIDS, and ease symptoms of post-traumatic stress disorder, the report concluded. But it said there’s not enough research to say whether they’re effective for treating cancers, irritable bowel syndrome, epilepsy, or certain symptoms of Parkinson’s disease, or helping people beat addictions.

Turning to potential harms, here are some of them listed in the report:

- Strong evidence links marijuana use to the risk of developing schizophrenia and other causes of psychosis, with the highest risk among the most HUFFPOST FOTO frequent users.

- Some work suggests a small increased risk for developing depressive disorders, but there’s no evidence either way on whether it affects the course or symptoms of such disorders, or the risk of developing post-traumatic stress disorder.

- Substantial evidence links pot smoking to worse respiratory symptoms and more frequent episodes of chronic bronchitis.

- There’s a weak suggestion that smoking marijuana can trigger a heart attack, especially for people at high risk of heart disease. But there’s no evidence either way on whether chronic use affects a person’s risk of a heart attack.

- Some evidence suggests a link between using marijuana and developing a dependence on or abuse of other substances, including alcohol, tobacco and illicit drugs.