After reviewing 80 randomized trials that included nearly 6,500 people, researchers found moderate support for using marijuana to treat chronic pain and muscle spasms and involuntary movements.

The evidence wasn't as strong to support marijuana's use for nausea and vomiting due to chemotherapy, sleep disorders, HIV-related weight loss and Tourette syndrome.

Also, any benefits of marijuana or cannabis use must be weighed against the risk of side effects, which include dizziness, dry mouth, nausea, sleepiness and euphoria, according to the study's lead author.

"Individuals considering cannabinoids as a possible treatment for their symptoms should discuss the potential benefits and harms with their doctor," said Penny Whiting of University Hospitals Bristol NHS Foundation Trust in the UK.