The shots didn't work perfectly, but the researchers say their limited success is promising enough to suggest the intriguing vaccine approach could be widely used to treat addiction within several years.
"It is such an important study. It clearly demonstrates ... that it is possible to generate vaccine that could interfere with cocaine actions in the brain," said Dr. Nora Volkow, director of the National Institute on Drug Abuse, which funded the study.
The results come just days after that government agency announced plans for the first late-stage study of an experimental nicotine vaccine designed to help people quit smoking. The NicVAX vaccine has been fast-tracked by the Food and Drug Administration, and the research will be paid for with federal stimulus money.
The cocaine and nicotine vaccines both use the same approach, stimulating the immune system to produce antibodies that attach to molecules of the drugs and block them from reaching the brain.
In the new study, cocaine-fighting antibodies helped prevent users from getting a euphoric high and led nearly 40 percent of them to substantially cut back or stop cocaine use at least temporarily.
With more than 2 million cocaine abusers nationwide and no federally approved treatment, the results "are good enough — better than having nothing," said lead author Dr. Thomas Kosten of Baylor College of Medicine in Houston. He developed the vaccine used in the study.
The study appears in October's Archives of General Psychiatry, released Monday.
Volkow said the research exemplifies a "transformative" perspective on drug addiction.
"By targeting it as a medical disease as opposed to a moral dilemma, we're likely to come up with solutions that have a much longer impact," she said.
The research involved 115 cocaine abusers also addicted to heroin who sought methadone treatment at a New Haven, Conn. clinic. Methadone treats heroin addiction, not cocaine, but it requires repeat clinic visits. That made it easier for the researchers to work with and track the cocaine abusers, Kosten said.
Over 12 weeks, nearly all participants got five shots of cocaine vaccine or a dummy substance. They were followed for an additional 12 weeks. All participants also attended weekly relapse-prevention therapy sessions, had their blood tested for antibodies and their urine tested for cocaine and heroin.
Overall, 21 vaccine patients — 38 percent — developed cocaine antibody levels high enough to prevent a cocaine high. In this group, 53 percent stopped using cocaine more than half the time during the study, versus 23 percent of those with lower antibody levels.
The researchers plan a larger study next year, Kosten said.
Despite the limited success, the results are exciting and show that the vaccine approach is a good one, said Dr. Kyle Kampman, a University of Pennsylvania addiction researcher who was not involved in the study.
"We need novel approaches because cocaine dependence is a disease that has been very difficult to treat," Kampman said.