Smoking marijuana helped relieve some multiple sclerosis symptoms in a small trial of 30 patients, a team of University of California-San Diego researchers reported in the Canadian Medical Association Journal on Monday.

Multiple sclerosis occurs when a person's immune system attacks the electrically insulating sheaths surrounding nerve fibers in the brain and spinal cord. Once the sheaths are damaged, nerve cell communications break down, resulting in a wide range of symptoms including spasticity -- stiffness or involuntary spasms that can cause pain and difficulty of movement.

Lead author Jody Corey-Bloom said in a telephone interview that she became interested in cannabis' effects on MS when patients told her that smoking a bit of marijuana before bed reduced their spasticity.

Honestly, I was a bit skeptical, she said.

There is already some scientific evidence showing that cannabis can help MS patients, but most of these papers focus on oral cannabis pills or nasal sprays, not smoked cannabis. And many of these studies rely more on subjective factors like reported levels of pain instead of objective measurements, according to Corey-Bloom.

In their trial, the UCSD researchers randomly gave patients either a marijuana cigarette or a placebo cigarette -- a cannabis cigarette with the THC, the active ingredient, extracted  -- once a day for three days. Before and after the subjects smoked, the researchers tested both their degree of spasticity and mental cognitive ability.

Then, after an 11-day waiting period, the two groups switched -- those that had smoked placebos then got an unaltered marijuana cigarette, and vice versa.

To measure changes in spasticity, Corey-Bloom and her colleagues used something called the Ashworth scale, which rates the degree of spasticity at a person's elbow, hip and knee joints. The scale ranges from 0 to 5, with 0 standing for no resistance to movement and 5 representing such severe spasticity that the joint won't bend.

The UCSD team found that the average Ashworth score for patients smoking the placebo cigarettes barely moved -- from 8.92 before treatment to 8.71 after they had smoked. But the average Ashworth score for patients that smoked marijuana with active THC dipped by about a third after treatment -- from 9.13 to 6.18.

It came at a price, though -- these patients were at least mildly cognitively impaired, Corey-Bloom said.

Still, the research paves the way for future trials comparing cannabis pills and sprays to the classic method -- which many people with MS seem to prefer.

Most patients say to me 'I don't want to take a pill or spray something in my mouth -- it's so much nicer to take a puff or two,' Corey-Bloom said.