Vaccine Raises Hope for Cocaine Addiction Therapy

CHICAGO (Reuters) - A vaccine helped block the high felt by cocaine users in 38 percent of people who took it, U.S. researchers said on Monday, offering promise of a new approach to treating those addicted to the drug.

The aim is to prevent cocaine's rewarding effects -- the high -- in order to reduce cravings that trigger drug relapses.

"The concept works," Dr. Thomas Kosten of Baylor College of Medicine in Houston, Texas, whose study appears in the Archives of General Psychiatry, said in a statement.

Cocaine molecules on their own are too small to draw the attention of the immune system. To get the body to recognize cocaine, the researchers designed a vaccine that uses a harmless version of the cholera toxin with a few attached cocaine molecules.

When the immune system reacts to the toxin, it makes both cholera and cocaine antibodies.

"These antibodies bind to the cocaine, preventing it from leaving the bloodstream," Kosten said. An enzyme called cholinesterase breaks down the cocaine and flushes it out of the body.

For the study, Kosten and colleagues studied 94 volunteers -- mostly users of crack cocaine, which is a solid, smokable form of the drug -- who were on methadone treatment at the Veterans Affairs Connecticut Healthcare System.

Over three months, the participants either got five shots of the vaccine or a placebo injection.

Those who had the highest antibody response were better able to stay cocaine-free. Although the vaccine does not wipe out cocaine cravings, it may help prevent relapse in some people, Kosten said.

The problem is that it does not create antibodies in everybody. "Twenty-five percent of the people who get the vaccine do not make much antibody response," he said.

Even so, the vaccine represents a "promising step toward an effective medical treatment," Dr. Nora Volkow, director of the National Institute on Drug Abuse, which is part of the National Institutes of Health, said in a statement.