It was the first test of the medicine in humans for cocaine addiction and involved only 20 addicts, so the work is considered preliminary. The drug has not been approved for use in the United States and can cause vision problems over the long term.
But experts were impressed and said more studies are called for.
Eight of 20 long-term addicts stopped using cocaine and haven't relapsed for 75 days or more so far, even though they stopped taking the medication a month ago, said psychiatrist Dr. Jonathan Brodie.
The drug was paired with psychosocial therapy, and the results are "startlingly good," said Brodie, a professor of psychiatry at New York University and lead study author.
Other authors included neuroanatomist Stephen Dewey of the Brookhaven National Laboratory in Upton, N.Y., who has studied the drug in animals. Called gamma-vinyl GABA, GVG or vigabatrin, it is used to treat epilepsy in other countries.
The cocaine study, published online Monday by the journal Synapse, was financed by NYU and the federal government.
Frank Vocci, a treatment expert at the National Institute on Drug Abuse, said the new study's success rate - 8 out of 20 - is comparable to that of other experimental cocaine treatment studies. But he said the prolonged period of abstinence "far exceeds what other pharmacological treatments have achieved."
Dr. James Halikas, a psychiatrist in Naples, Fla., who serves on the board of the American Society of Addiction Medicine, called the work "an important beginning" that must be followed up by further research.
"I think this drug has a lot of potential," said Halikas, who was not involved in the study.
The addicts who participated in the study, conducted at a drug treatment center in Mexicali, Mexico, had used cocaine for an average of 12 years. They took GVG twice a day in escalating doses until urine samples showed they were cocaine-free for four consecutive weeks. Then the medicine doses were gradually tapered off, for a total regimen of about 10 weeks for most of them.
Eight addicts dropped out of the study within 10 days, saying they wanted to keep using cocaine. Four others stayed in the experiment for varying lengths of time, with three of them reducing their cocaine use by 50 percent or more. The eight addicts who completed the program stopped using altogether and reported that they'd stopped craving cocaine some two to three weeks after they started taking GVG.
GVG blocks cocaine's "high" by raising the concentration of a calming brain chemical called GABA, Brodie said.
Its most worrisome potential side effect is a loss of peripheral vision. That has been reported in 30 percent to 40 percent of people who've taken far more GVG than the cocaine study used, and typically after years of use, Brodie said.
The researchers didn't check for the visual problem because their study was so brief, but it should be addressed in future research on GVG for cocaine treatment, Brodie said.
By Malcolm Ritter