Medicine Man.

Beyond the circle of lantern light, the darkness is absolute. Daniel Mattin (not his real name), sitting cross-legged in a small hut, listens to the freakishly loud chorus of tropical birds and trees rustling in the night breeze. A shaman wearing a jumble of necklaces and emblems chants icaros, or songs, to summon the "spirit of the plant"--in this case an ayahuasca, a species native to the Peruvian Amazon and purported to evoke mystical experiences. Minutes after Mattin imbibes ayahuasca-infused brew, the "spirit" catches him. He sees elephants adorned with jewels and crowns, and a dwarf performing magic tricks. Some of the hallucinations are harmless enough, but others, like the image of women's rotting genitals, are terrifying. Mattin, though, interprets them as healing messages. "Yes, you touch your dark side," he says. "But you have to in order to get to the light." Eventually, Mattin finds what he believes he had been looking for all along: Jesus Christ and the Virgin Mary appear before him, as palpable as anybody he'd ever met.

Until that moment, Mattin, 21, didn't know what he was looking for. That had always been part of his problem. At 13, he acquired an addiction to cocaine. By his last year of high school, he was getting high at least five days a week--bingeing on cocaine or barbiturates, and dabbling in heroin. "I thought I was nobody without drugs," he says. A psychiatrist prescribed an antidepressant, which may have hastened his downward spiral. When he hit rock bottom, he enrolled at Takiwasi, a drug treatment center on the edge of the Peruvian Amazon. Mattin's religious awakening came during the course of dozens of treatments over 10 months ending in May. It was a turning point in his life--at least he's convinced it was. Mattin has gone a year without illegal drugs, and in August his psychiatrist stopped the antidepressants.

Mattin credits his recovery to Jacques Mabit, a French physician who founded the Takiwasi clinic 10 years ago near the remote town of Tarapoto in Peru. Since then, he claims to have successfully treated scores of former addicts with ritual fasting, psychotherapy and hallucinogenic-drug trips. Nearly all his patients undergo a mystical or religious awakening.

The notion of using hallucinogenic drugs sounds like a relic of the 1960s, but recently scientists have taken a fresh look. Research on ecstasy, psilocybin and other drugs is ongoing in dozens of universities in the United States and Europe. Scientists believe that psychotropic drugs may yield therapeutic benefits for drug addicts and those suffering from chronic depression, and that studying their effects may yield insight into how personality is constructed in the brain. "There is tremendous potential there in terms of future research," says Charles Grob, a psychiatrist at UCLA.

Depending on your point of view, Mabit is either at the forefront of this research or he's careering dangerously ahead of it. Research on psychotropic drugs is many years from clinical trials, but Mabit isn't waiting for the tests: he's already using hallucinogens on live patients. The practice is controversial, to say the least. Critics contend that he's endangering the lives of his patients without any good science to back up his claims. Back in France, where Mabit gets many of his referrals, he's been suspected of being involved in a "sect." Mabit says he's simply picking up where conventional medicine has failed. Is he a visionary who's anticipating where medical science is headed? Or is he, as critics charge, a danger to the desperate and vulnerable young adults he lures to his treatment center in the jungle?

Mabit, a portly 47-year-old who speaks reassuringly like a country doctor, first went to Peru in the 1980s with the French group Doctors Without Borders. Native healers told him about how they used plants to cure rheumatism and mental illness. They would talk about how the plants "taught" them how to heal, or "told" them what a particular patient needed. "They told me that if I really wanted to understand how the plants worked, I would have to try them," says Mabit. During several months, Mabit underwent several ayahuasca sessions with local ayahuasceros, or healers. ...