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A balm for pain

August 18, 2008|Jill U. Adams | Special to The Times

Medical marijuana use has a history stretching back thousands of years. In prebiblical times, the plant was used as medicinal tea in China, a stress antidote in India and a pain- reliever for earaches, childbirth and more throughout Asia, the Middle East and Africa.

In recent decades, medical researchers have investigated marijuana's effects on various kinds of pain -- from damaged nerves in people with HIV, diabetes and spinal cord injury; from cancer; and from multiple sclerosis. Marijuana has also been hypothesized to help with nausea induced by chemotherapy and antiretroviral therapy, and with severe loss of appetite as seen in people with the AIDS wasting syndrome.

The weed's actions are due to the active ingredients tetrahydrocannabinol (THC) and some 60 other cannabinoids, which mimic the action of chemicals -- known as endogenous cannabinoids -- that exist naturally in the brain. Those cannabinoids activate receptors in our nerves, triggering physiological responses.

A legal prescription form of THC (Marinol) exists, yet researchers say it's far from a perfect drug. Taken orally, its absorption is highly variable and unpredictable and often delayed, says Dr. Igor Grant, a UC San Diego psychiatrist who directs the university's Center for Medicinal Cannabis Research. "Smoking is a very efficient way to deliver THC," he says.

As a result of its federally illegal status, medicinal use of marijuana is restricted to carefully vetted clinical research studies or to patients in states such as California that have passed laws to allow for personal medical use. Research on the medicinal use of marijuana relies on government-issued marijuana cigarettes, which come in different strengths and are supplied by the National Institute on Drug Abuse.

The UC Center for Medicinal Cannabis Research in San Diego helps coordinate clinical studies to investigate the safety and effectiveness of marijuana. Here's what they've found.

Neuropathic pain

Recent research suggests that marijuana can assuage this chronic-pain syndrome in which burning sensations occur and simple touch can feel like hurt. It is unaffected by aspirin-like drugs and fairly resistant to stronger analgesics such as opiates.

In a 2007 study on neuropathic pain related to HIV infection, 50 patients smoked marijuana cigarettes three times a day or marijuana cigarettes from which active ingredients had been extracted. Subjects then rated their pain on a scale ranging from "no pain" to "worst pain imaginable." The results, published in the journal Neurology, showed a 34% reduction in ratings of pain in the marijuana group compared with 17% in the placebo group over five days of treatment.

Another study in 44 patients reported in June in the Journal of Pain found that marijuana alleviated neuropathic pain arising from a variety of conditions, including spinal-cord injury and diabetes. Participants smoked marijuana on a set schedule -- first two puffs, then three puffs an hour later, then four puffs an hour after that -- from a single cigarette containing either 0%, 3.5%, or 7% THC. Average pain ratings before smoking were 55 on a 100-point scale and decreased by 46% in both treatment groups and by 27% in the placebo group one hour after the last puff.

Analgesic drugs are often tested against experimentally induced pain. Such studies have been conducted for marijuana too. In one 2007 report in the journal Anesthesiology, 15 healthy volunteers received skin injections with capsaicin -- the chemical behind that fiery spice in chile peppers -- and then smoked different-strength marijuana cigarettes. The medium dose, with a 4% THC concentration, lessened the burning pain.

These three pain studies all concluded that smoked marijuana can bring relief to sufferers of neuropathic pain comparable to other analgesic drugs. It is not a cure, Grant says: "It's like other pain medicines, you have to keep taking it."

Study subjects did feel high, an effect that varied among individuals. Marijuana also affected thinking, shown as problems with tasks of memory and complicated reasoning after the strongest marijuana cigarettes were used. Potentially problematic, these effects were tolerated by subjects -- no one opted out of the study because they couldn't think straight.

Grant says it's important to have a choice of treatments because not everyone responds to or can tolerate the available drugs. Antidepressants are used for neuropathic pain but cause dry mouth, constipation and urinary problems, and must be avoided by people with conditions such as glaucoma. Others can't take aspirin-like drugs. "Having an alternative compound is always good," Grant says.

Multiple sclerosis

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