People with chronic pain from across Canada are being recruited for a study that aims to determine the safety of medical marijuana.

In the COMPASS study, researchers at Montreal's McGill University will follow 1,400 patients with chronic pain.

The cannabis used in the study contains about 12 per cent of the active ingredient, THC.
The cannabis used in the study contains about 12 per cent of the active ingredient, THC.

Of the participants, 350 will use research-grade medical marijuana as part of their pain management strategy for one year.

"Patients in COMPASS will typically have pain resulting from spinal cord injuries, multiple sclerosis, arthritis or other kinds of hard-to-treat neuropathic or muscle pain," said Dr. Mark Ware, the study's principal investigator.

Cancer patients are not eligible, said Ware, a pain physician at the McGill University Health Centre.

At the beginning and end of the study, participants will do tests to help researchers determine whether the drug affects cognitive functions.

Investigators will look at safety issues such as side-effects, kidney, liver, heart and lung function and hormone levels.

While previous studies have looked at whether cannabis relieves pain and other symptoms, the safety study is unique.

The research is needed to understand safety issues, particularly among patients who take several medications or have other diseases like diabetes or high blood pressure.