The drinkers were rats, selectively bred for their liking for the hard stuff. Researchers from the University of North Carolina who carried out the experiments, plan to test it next on human alcoholics.
Dr Amir Rezvani, research associate professor of psychiatry at the university's school of medicine, said: "We don't know yet whether the compound will work in human alcoholics, but we are optimistic.
"Since it is a herb, it should have no side effects or fewer side effects than synthetic drugs. One of the major problems with alcoholics is that they don't like to take medications that have side effects. St John's wort might be different in that it would just reduce their desire for alcohol."
Dr Rezvani decided to investigate the herb because depression and alcoholism were thought to have a strong biological link. "If it worked for depression, then it might just have a beneficial effect on alcoholism," he said.
"Many people think the link may be a deficiency of serotonin, a neurotransmitter in the brain."
The findings were presented yesterday at a meeting of the Research Society on Alcoholism in Hilton Head, South Carolina.
The researchers compared the behaviour of rats that were given the extract and another group that was not. All were offered a choice between alcohol and water.
Over a 24-hour period the rats treated with the herbal extract drank half as much alcohol as the untreated animals.Reuse content