Canadian researchers say vaping medical marijuana failed to ease breathlessness in the majority of COPD patients in their study.

Researchers tracked outcomes for 16 people with advanced COPD who were already taking medications for their lung disease. The patients inhaled either a single dose of vaporized cannabis or a placebo before exercising on a stationary bike.

For most people in the trial, vaporized cannabis had no clinically significant effect — either negative or positive — on their symptoms of breathlessness during exercise or on their exercise performance, the Montreal team reported.

Only 4 of the 16 participants noted some improvement of breathlessness after using the vaped product, the researchers said, while the other 12 showed no effect or felt worse.