"Research suggests that people may be using cannabis as an exit drug to reduce use of substances that are potentially more harmful, such as opioid pain medication," said the study's lead investigator Zach Walsh, associate professor of psychology at UBC's Okanagan campus.

This comprehensive review of research on medical cannabis use and mental health also found some evidence that cannabis may help with symptoms of depression, PTSD and social anxiety. However, the review concluded that cannabis use might not be recommended for conditions such as bipolar disorder and psychosis.

"In reviewing the limited evidence on medical cannabis, it appears that patients and others who have advocated for cannabis as a tool for harm reduction and mental health have some valid points," said Walsh.

Walsh and his team reviewed all studies of medical cannabis and mental health, as well as reviews on non-medical cannabis use -- making the review one of the most comprehensive on the topic to date.

With legalization of marijuana possible as early as next year in Canada, it's important to identify ways to help mental health professionals move beyond stigma to better understand the risk and benefits of cannabis, added Walsh.

"There is currently not a lot of clear guidance on how mental health professionals can best work with people who are using cannabis for medical purposes," said Walsh. "With the end of prohibition, telling people to simply stop using may no longer be as feasible an option, so knowing how to consider cannabis in the treatment equation will become a necessity."

Walsh's research was conducted with UBC's Michelle Thiessen, Kim Crosby and Chris Carroll, Raul Gonzalez from Florida State University, and Marcel Bonn-Miller from the National Centre for PTSD and Center for Innovation and Implementation in California.

The study was recently published in the journal Clinical Psychology Review.