In a Canadian study, smoking marijuana reduced pain and improved the sleep of patients suffering from chronic neuropathic pain.

Neuropathic pain is a term broadly and loosely used to describe pain whose exact source or cause cannot be pinpointed. In this study, the patients' pain stemmed from events such as traffic accidents or surgery where nerves had presumably been cut. Because it's hard to pinpoint the exact source of the pain, it's also hard to treat it. Like the patients in this study, sufferers of neuropathic pain often get little relief from traditional treatments for pain.

The total THC dose used in the study was kept low, to minimize side effects and exposure to smoke. And the low dose also helped keep participants in the dark about what preparation they were using in each cycle, minimizing euphoric and other psychoactive effects.

In the study, subjects given a placebo (no THC) reported an average pain intensity of 6.1 on an 11-point scale. This intensity dropped to 5.4 in those who smoked marijuana containing 9.4% THC. THC is the active ingredient in marijuana.

While other studies have tested the ability of marijuana to relieve pain, the researchers say this is the first study where patients were allowed to smoke cannabis at home and record their responses daily.

The study was performed on 23 adults, aged 25-77. Their average age was 45. Study subjects were randomly assigned to smoke marijuana with a THC content of 0, 2.5%, 6.0% and 9.4% during four rotating 14-day periods. Each period consisted of five days taking the drug followed by a nine-day washout period (no drug). Marijuana was administered as a 25 mg dose smoked in a pipe, three times daily, by the study subjects.

The main interest of the researchers was in testing the effect of smoking marijuana with 9.4% THC on pain. The results suggest modest, but noticeable, pain relief.

The total THC dose used in the study was kept low, to minimize side effects and exposure to smoke. And the low dose also helped keep participants in the dark about what preparation they were using in each cycle, minimizing euphoric and other psychoactive effects. Overall, marijuana was well tolerated by the subjects.

Medical marijuana use is legal in Canada. In the U.S, such usage and even marijuana research itself has been limited. The reasons for this are at least as much political and sociocultural as they are medical.

Federal law prohibits marijuana use. In 1996, California passed a law allowing medical marijuana to be used by people who had a doctor's prescription for it. More than a dozen states have since passed similar laws. But the Bush Administration declared medical use of marijuana to be in violation of federal law and took vigorous action against it, including the raiding of dispensaries. Soon after the election of Barack Obama, the Department of Justice announced it would cease these raids, as long as the dispensaries were abiding by state law. It's anybody's guess what policies will be in effect in the near and far future.

The Canadian study was a very short term one: it only measured pain relief over five days. And it only tested low doses. The researchers emphasize that larger and longer studies need to be done to better evaluate the usefulness and long term safety of marijuana as a pain reliever. What the study does suggest is that marijuana can be useful at relieving the pain of a group of people for whom other pain relievers do not do the job.

An ahead of print article detailing the study was published online by the Canadian Medical Association Journal on August 30, 2010 and is freely available.