A Saskatoon-based company is leading the first-ever Health Canada-approved clinical trial of medical marijuana.

CanniMed and its parent company Prairie Plant Systems of Saskatoon recently announced that it is looking for 40 people over age 50 suffering from serious osteoarthritis of the knee.

The study is expected to take anywhere from 12 to 18 months, Prairie Plant Systems CEO Brent Zettl said.

"We're looking for the side effects that physicians could watch for," Zettl said. "We want to have that quantified and characterized better."

Most of the information on medical marijuana is anecdotal, Zettl said. Data from the study should be released in three years, he said.