Heroin and cocaine have been tested on mice and other laboratory animals. But Columbia's study is now the only one in the country testing addicts with heroin, although researchers at Harvard have done so and researchers at Johns Hopkins plan to. Dr. Marian W. Fischman, a psychologist at Columbia who studies medications for drug abusers, said the volunteers, who agree to stay in the hospital for six or seven weeks, had rejected offers to treat their heroin habit. We refer anyone to treatment who would even moderately consider it. The medications being tested affect the brain different ways.
Naltrexone is an antagonist, meaning that it blocks the effect of heroin on the brain's receptors.
Methadone is an agonist, which stifles the craving for heroin by binding to the brain receptor. The third, buprenorphine, acts as an agonist at lower doses and as an antagonist at higher doses. Unlike methadone, naltrexone could be available with just a doctor's prescription. But because a dose lasts only a day or so and leaves some users feeling anxious and unhappy, many tend to quit. Fewer than 2,000 heroin addicts nationwide take naltrexone, compared with 115,000 methadone users.