People who suffer from a medical disorder that causes chronic pain are buying marijuana on the street for relief, a new study has revealed.

The study, led by Dr. Mary-Ann Fitzcharles, a rheumatologist at the McGill University Health Centre in Montreal, appears in the journal Arthritis Care & Research.

It shows that 13% cent of patients living with fibromyalgia (FM) use cannabinoids for relief from symptoms such as widespread pain, fatigue, and insomnia, and 10% buy cannabis illegally for these reasons. It says these people tend to have poorer mental health, and are often on additional prescribed medications that could result in negative drug interactions. Cannabinoids are a type of chemical in marijuana that causes drug-like effects all through the body, including the central nervous system and the immune system.

"Fibromyalgia affects up to three per cent of the population and is more common in women," says Dr. Fitzcharles, who is also a professor of medicine at McGill University. "Unfortunately, FM pharmacologic treatments for pain have modest results, prompting some patients to self-medicate with more non-traditional therapies, such as marijuana."

Dr. Fitzcharles says she and her colleagues assessed cannabinoid use in 457 FM patients being treated at the MUHC Alan Edwards Pain Management Unit. They determined that 13% of participants used cannabinoids to help manage pain, fatigue, and insomnia, and 10% cent bought cannabis illegally.

Men were more likely to turn to marijuana more than women, and marijuana users were more likely to have an unstable mental illness and display opioid drug-seeking behaviour. Additionally, marijuana users had a 77% unemployment rate, which researchers believe may be a result of ineffective pain control or a more serious functional disability.

"While self-medicating with cannabinoids may provide some pain relief to fibromyalgia patients, we caution against general use of illicit drugs until health and psychosocial issues risks are confirmed," says Dr. Fitzcharles. "Physicians should also be alert to potential negative mental health issues with these patients using illicit drugs for medical purposes, and that some cannabis users may be dishonestly using a FM diagnosis to justify self-medicating with illegal drugs."