An experimental vaccine helped 38 percent of people in a trial end their addictions to cocaine, according to a news release from the National Institutes of Health.

The vaccine causes the body's immune system to produce antibodies. Instead of destroying a virus or bacteria, in this case they bind to cocaine molecules, which makes them unable to pass into the brain. That means that people who take cocaine can't feel it.

The study looked at 115 patients in treatment for drug addiction. Half were given the new treatment, and half were given a placebo. All of the patients also had weekly counseling sessions and were tested three times a week for drug use.

Researchers said that those whose bodies produced the most antibodies were most likely to have clean tests.

"Fifty-three percent of participants in the high-antibody group were abstinent from cocaine more than half the time ... compared with only 23 percent of participants with lower levels of antibodies," said Dr. Thomas Kosten of Baylor College of Medicine in Houston.

But he noted that the immunization did not cause complete abstinence.

The study was published in the October issue of the Archives of General Psychiatry.