STEVE INSKEEP, Host:
NPR's Joe Palca reports.
JOE PALCA: Salvia divinorum is a plant. It's a member of the mint family. Smoking it sends users on an otherworldly voyage.
MATTHEW JOHNSON: Some people would speculate that it's another dimension. Others would describe it as the spirit world.
PALCA: For example, people on the drug psilocybin - what makes magic mushrooms hallucinogenic - are aware of the real world around them and can function in it. During the brief-but-potent high, people on salvia can barely move, and they feel as if they've left planet Earth.
JOHNSON: A completely different reality where they're interacting with things they're either calling entities or angels or figures that have even given themselves names in this otherworldly experience.
PALCA: Johnson wanted to see if there were any physical side effects to this mental trip. So he invited people who had used other hallucinogens to try salvia and looked to see if there were any potentially harmful spikes in heart rate or blood pressure.
JOHNSON: Under the conditions of the study, it did appear to be a physiologically safe drug.
PALCA: At least for the things Johnson measured. But he says while the drug may not be harmful physically, it can be mentally.
JOHNSON: There's the psychological toxicity. That is to say, this is a strong drug and people can do strange, potentially dangerous things when they're on it.
PALCA: Salvia belongs to a class of drugs that activate something called the kappa opioid receptor. Heroin and morphine also activate opioid receptors, but they activate the mu opioid receptor.
ELENA CHARTOFF: When you activate the mu receptor, like you do with heroin or morphine, you get a euphoric - you get a rush, a high.
PALCA: Elena Chartoff studies opioid receptors at McLean Hospital in Boston.
CHARTOFF: But when you activate the kappa receptor with a drug, you get kind of the opposite effect, that depressive-like effect.
PALCA: Salvinorin A, the active ingredient in salvia, has a powerful effect on the kappa opioid receptors. Chartoff says scientists are looking at ways to take molecules like Salvinorin A...
CHARTOFF: And altering them using a chemistry to develop compounds that have all the beneficial properties, but don't have the disadvantages.
PALCA: Hallucinations are generally considered an unwanted side effect in drug therapies. But pharmacologist Bryan Roth of the University of North Carolina says those properties may be useful for neuroscientists.
BRYAN ROTH: One of the things to me that's interesting about drugs that are hallucinogens is they alter the way we see reality.
PALCA: Roth is trying to figure out which brain circuits Salvinorin A acts on - where in the brain we decide what's real and what's not.
ROTH: You know, what could be more important than how we view reality, right?
PALCA: Joe Palca, NPR News, Washington.