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MONDAY, April 16 (HealthScout) -- A synthetic drug has the effect of helping the brain say "no" to marijuana, new research shows.
The drug effectively dulls the effects of smoked marijuana and might be useful in treating people addicted to the illegal substance, the study says.
The drug, SR141716, mutes the effects of marijuana by more than 40 percent by locking up receptors in the brain for the drug's active ingredient, tetrahydrocannabinol (THC). A report on the findings, by government researchers, appears in the current issue of the Archives of General Psychiatry.
THC belongs to a family of chemicals called cannabinoids -- from the Latin word for marijuana, cannabis -- which interact with protein receptors on the surface of brain cells. Neurons that respond to cannabinoids, which the body also produces, are involved in several functions, including memory, learning and appetite, and the immune system.
Researchers have shown in animals that a drug that blocks one of the cannabis receptors, called CB1, can dull the reaction to marijuana. The latest work is the first to repeat those experiments in human marijuana users, says Marilyn Huestis, a drug metabolism expert with the National Institute on Drug Abuse.
Huestis, who led the study, and her colleagues first gave 63 male marijuana users varying doses of either the pot-blocking drug or a placebo. Two hours later the men, ages 21 to 45, smoked cigarettes rolled from government-grown pot with a tightly controlled THC content, and sham joints stripped of the chemical.
A high 'blockade'
Low doses of SR141716 didn't blunt the effects of the marijuana very well. But men who took 90 milligrams, the highest dose, reported feeling about 40 percent as "high," "stoned" and affected by the drug as those who didn't get the pot blocker.
"If you give higher doses or if you give multiple doses you can get more of a blockade," says Huestis.
Marijuana also speeds up the heart, but the men who took 90 mg of the THC blocker had about 60 percent less of an increase in beat rate as those who had marijuana alone.
Marijuana addiction is a controversial phenomenon, and many advocates of the drug insist that while pot may be habit-forming, it's not strictly addictive. Huestis, however, says pot "can be addictive for some people," and, referring to SR141716, adds that "it's nice that this tool is there" to treat those hooked on the narcotic.
But Dr. Joseph Palumbo, who oversees SR141716 at Sanofi-Synthelabo, says the drug's most promising application will be not in drug treatment clinics but in weight loss centers. That's because cannabinoid receptors appear to play an important role in modulating feelings of hunger and satiety, and a study released last week showed that the drug can suppress appetite markedly in mice.
Palumbo says the company is organizing a study of the compound in obese patients.
What To Do
To learn more about drug abuse, visit the National Institute on Drug Abuse. The agency also has a Web site on teen use of marijuana.
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