"It produces a remarkable state of non-defensiveness and heart-openness, and I think that's a very useful thing for people to realize they've got that potential," he says. "It's a very good teaching tool, but has to be used in the right session and it's not something that you do all the time. It's something you learn from."

Weil may be just one step ahead of his more traditional medical community colleagues. Just four days after our Nov. 1 interview The Wall Street Journal reported that the Food and Drug Administration has approved the first study of MDMA as a treatment for people with posttraumatic stress disorder.

Weil has repeatedly shown that he isn't afraid to take an unconventional stance on controversial issues. Not only has Weil taken a neutral stance on many banned substances, he has always felt it his medical duty to personally test them as well.

But Weil's conclusions are not frivolously reached. He has spent most of his adult life studying plants, nutrition and their effects, positive and negative on human health.

His undergraduate degree from Harvard was in botany, a real backwater in the early 1960's. Six years later, at Harvard medical school, Weil conducted the first double-blind study on the effects of marijuana. Weil managed to obtain samples of the plant legally, from the federal government, because his Harvard supervisors vouched for his impeccable anti-drug credentials. After all, six years earlier Weil had uncovered a major drug scandal at Harvard. As an undergraduate journalist for the Harvard newspaper The Crimson, Weil broke the story on Professors Richard Alpert and Timothy Leary's unsanctioned experiments with the hallucinogen, LSD.

In 1972, Weil published The Natural Mind: An Investigation of Drugs and the Higher Consciousness. He then embarked on a tour of central and South America, where he not only studied plants but indigenous peoples, their medicine and pharmacology.

What struck him most was the prevailing attitude toward drugs. He describes Indian tribes in the Amazon where each household has an abundance of coca leaves (the derivative for cocoaine) available, yet children expressed absolutely no interest in taking the drug.

"One of the things we've done foolishly is that we've made these drugs intensely interesting to young people by forbidding them and exaggerating their dangers. And it's very interesting to be in a culture where there's zero curiosity on the part of kids about these substances, and in that tribe there were no laws regulating that usage. There was a group consensus, a process of social learning."

Weil's words are taken seriously by the medical community. He has been a groundbreaker when it comes to combining nutrition, stress reduction and holistic, or what he calls "integrative", health. Those who once scoffed at his marijuana studies have seen his efforts vindicated by growing acceptance of the drug's medicinal purposes. But if that drug's road to legalization is any indicator, we won't be seeing Ecstasy on drug store shelves any time soon.

Watch for more of the Andrew Weil interview on an upcoming episode of MyPrimeTime's "Great Leaders" TV series on PBS. The show airs in local markets in late January; check your local listings for show times.