A study conducted by researchers at the University of British Columbia claims that marijuana could help treat substance abuse and mental health illnesses such as depression, PTSD and social anxiety.

Although marijuana or cannabis remains illegal in many states in the U.S., it remains the most commonly used illicit drug in the country with around 22.2 million users in the past month, Medical News Today reported.

To come up with an assessment, Walsh and his team reviewed 60 different studies about medical and non-medical use of marijuana. Eurekalert notes that the review is one of the most comprehensive reports to date on the effects of medical cannabis on mental health.

"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," says the study's lead investigator Zach Walsh, an associate professor of psychology at UBC's Okanagan campus.

How does cannabis treat addiction? According to the researchers, cannabis may act as a replacement, particularly for heavy opioid users.

"Research suggests that people may be using cannabis as an exit drug to reduce the use of substances that are potentially more harmful, such as opioid pain medication," says Walsh.

Walsh told SF gate in a separate interview that the recent finding could help address the opioid epidemic in the US.

"We are really excited about the potential substitution effect," said Walsh. "If people use cannabis as a replacement for opioid medications, or to get off of opioids or cut back, we could see some pretty dramatic public health benefits. The level of opioid overdoses is so high right now."

American Society of Addiction Medicine cites that drug overdose is the leading cause of accidental death in the US, with 47,055 lethal drug overdoses in 2014. There were 18,893 overdose deaths related to prescription of opioid pain relievers in the same year.

Meanwhile, their study also revealed that for patients with psychotic disorders such as bipolar disorder, non-medical marijuana use may be problematic while medical marijuana does not raise the risk of self-harm or harm to others.

The study was published In the journal Clinical Psychology Review.