OTTAWA, Canada — Smoking cannabis can relieve chronic neuropathic pain and help sufferers sleep, researchers said in a study published in the Canadian Medical Association Journal on Monday.

Smoking pot also improved their mood, said the researchers led by Mark Ware at McGill University in Montreal.

Twenty-one participants in the study were asked to inhale marijuana smoke three times daily for five days.

Each suffered from post-traumatic or postsurgical neuropathic pain, caused by nerves that do not heal, for which there are few treatment options.

"A single inhalation of 25 mg of 9.4 percent tetrahydrocannabinol herbal cannabis three times daily for five days reduced the intensity of pain, improved sleep and was well tolerated," the study concluded.

Less potent cannabis yielded "intermediate but nonsignificant degrees of relief," it added. "We found no differences in mood or quality of life" in those cases.

The most common adverse effects of the drug -- found to be negligible -- were headaches, dry eyes, a burning sensation in areas of neuropathic pain, dizziness, numbness and coughing.