Scientists are taking a fresh look at salvia -- the controversial drug that can cause an intense psychedelic experience -- as a potential treatment for an array of neurological disorders, including addiction.
Smoking the herb, which is related to mint, has been chronicled in countless YouTube videos. Now, researchers at Johns Hopkins University Medical School say it could open the door to a whole new class of drugs that have powerful analgesic properties.
This is the first controlled study in humans on the effects of salvinorin A, the active ingredient in the plant salvia divinorum -- the most powerful hallucinogen in nature.
The study showed that the drug has no physically adverse effects on otherwise healthy people.
Lead researcher Matthew W. Johnson, a psychologist and assistant professor of psychiatry, said the study was an attempt to "put some rigorous scientific information into current concerns over the growing recreational use" of salvia.
The study findings are published online in the journal Drug and Alcohol Dependence.
"We did document the very intense nature of the drug, even among those who are used to strong hallucinogenic drugs," Johnson told ABCNews.com. "That in itself is an area of danger -- people can have accidents or do foolish things on the drugs."
"But it's a remarkably robust drug in terms of physiological safety," said Johnson. "But behavioral safety, that's another dimension."
Most of the understanding of salvia has come from YouTube videos and not scientific studies.
Johnson said learning about salvia's effects on the brain could lead to medical advances in the treatment of Alzheimer's disease, chronic pain and, though it seems counterintuitive, drug addiction.
"It might be a longer-acting version of the drug and one without the strong psychedelic effects, just the analgesic effects," he said. "We have done the first human study with the drug and it could be the first examination fo a whole new line of drugs that have a therapeutic potential."
Animal studies have shown that salvinorin A activates opioid receptors in the brain, which are responsible for the high a person gets from drugs like heroin and opium.
But addictive drugs work by stimulating what scientists call mu opioid receptors. Salvinorin A works on the kappa opioid receptors, which have a depressive effect if activated.
"Heroin, morphine, oxycontin, the traditional pain killers all hit the mu opioid," said Johnson. "But salvinorin A selectively hits the kappa receptors and it hits them more cleanly than any drugs have before."
The kappa receptors are associated with a strong analgesic response, but not the pleasure response that can cause addiction.
"It is the opposite of the addictive effect," he said. "Most animal models make it look like more of a punisher than a reinforcer."
In the study, humans, too, report that the drug is "too intense," according to Johnson. "It's bizarre, people say they just don't want to do it again."
The study was small and in a controlled medical environment. It involved four volunteers, two men and two women, who had experience with hallucinogens.
The participants, who were allowed to drop out of the study at any time, smoked the drug in 20 sessions over two to three months, inhaling a range of doses of the drug in its pure form and rating its strength.
None withdrew from the study, but they were allowed to take breaks from the drug when sessions were too intense.