Marijuana: The good, bad and unknown about pot's health effects

Flowering marijuana plants are pictured during a tour of Tweed in Smiths Falls, Ontario on Thursday, Jan. 21, 2016. (Sean Kilpatrick / THE CANADIAN PRESS)

NEW YORK -- It can almost certainly ease chronic pain and might help some people sleep, but it may also raise the risk of getting schizophrenia and trigger heart attacks.

Those are among the conclusions about marijuana reached by a federal advisory panel in a report released Thursday.

The experts also called for a national effort to learn more about marijuana and its chemical cousins, including similarly acting compounds called cannabinoids.

The current lack of scientific information "poses a public health risk," said the report from the National Academies of Sciences, Engineering and Medicine. Patients, health care professionals and policy makers need more evidence to make sound decisions, it said.

For marijuana users or those considering it, "there's very little to guide them" on amounts and health risks, said Dr. Marie McCormick of the Harvard School of Public Health, who headed the committee.

Several factors have limited research. While the federal government has approved some medicines containing ingredients found in marijuana, it still classifies marijuana as illegal and imposes restrictions on research. So scientists have to jump through bureaucratic hoops that some find daunting, the report said.

A federal focus on paying for studies of potential harms has also hampered research into possible health benefits, the report said. The range of marijuana products available for study has also been restricted, although the government is expanding the number of approved suppliers.

Twenty-eight states and the District of Columbia have legalized marijuana for a variety of medical uses, and eight of those states plus the district have also legalized it for recreational use.

The report 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.

There may be more evidence soon: a study in Colorado is investigating the use of marijuana to treat PTSD in veterans.

Turning to potential harms, the committee concluded: