What I did that day should not be illegal. Adults seeking solace or insight ought to be allowed to consume psychedelics such as LSD, psilocybin, and mescaline. U.S. laws now classify them as Schedule 1 drugs, banned for all purposes because of their health risks. But recent studies have shown that psychedelics—which more than 20 million Americans have ingested—can be harmless and even beneficial when taken under appropriate circumstances.

Citing this research, some scholars and scientists are proposing that the prohibitions against psychedelics—or entheogens, "God engenderers," as believers in their spiritual benefits prefer to call them—should be reconsidered. This legal issue has recently been brought to a head by a religious sect in New Mexico that is suing the United States for the right to drink a hallucinogenic tea called ayahuasca in its ceremonies. A federal court is expected to rule on the potentially momentous case any day now.

"There is no doubt that hallucinogens can be used unwisely," says Charles Grob, a psychiatrist at the UCLA-Harbor Medical Center, who testified in the ayahuasca case and is a leader of the effort to rehabilitate the reputation of these substances. "But these studies show that they can be used safely within certain parameters."

After LSD's astonishing effects were discovered by the Swiss chemist Albert Hofmann 60 years ago, many psychiatrists considered it and similar compounds potential treatments for psychological ailments. That is why the psychiatrist Humphrey Osmond called the drugs "psychedelic," from the Greek root for "mind-revealing." By the mid-1960s, medical journals had published more than 1,000 papers describing the treatment with psychedelics of some 40,000 patients afflicted with disorders ranging from schizophrenia to alcoholism.

One remarkable study from this period, known as the Good Friday experiment, probed the capacity of psilocybin (the active ingredient of so-called magic mushrooms) to trigger spiritual experiences. On Good Friday, 1962, the Harvard psychiatrist Walter Pahnke dispensed psilocybin and placebos to a group of 30 divinity students and professors assembled in a Boston church. A majority of those who received psilocybin reported sensations of profound awe and self-transcendence that had lasting positive effects.

By the early 1970s, the surging popularity of psychedelics among the young—urged by Timothy Leary to "turn on, tune in, and drop out"—had triggered a backlash. Psychedelics were outlawed, and virtually all research on them was shut down amid rising concerns about their adverse social and medical effects. In 1971, the Journal of the American Medical Association warned that repeated consumption of psychedelics would usually result in permanent "personality deterioration."

Further research has shown these fears to be exaggerated, says John Halpern, a psychiatrist at Harvard Medical School. To be sure, psychedelics can cause acute and sometimes persistent psychopathology, especially in those predisposed to mental illness. But Halpern maintains that these compounds are usually harmless when ingested by healthy individuals in appropriate settings.

As evidence, Halpern cites a five-year study he recently completed with a Harvard colleague of members of the Native American Church, who are permitted by U.S. law to consume the mescaline-containing cactus peyote as a sacrament. Church members who had taken peyote at least 100 times showed no adverse neurocognitive effects compared to a control group.

Similar results have emerged from a study of ayahuasca by UCLA psychiatrist Grob and other scientists, results that Grob describes in the essay collection Hallucinogens. Ayahuasca, a tea brewed from two Amazonian plants, contains the potent psychedelic dimethyltryptamine, or DMT. Although the tea often triggers nausea and diarrhea, Indian shamans have prized it for its visionary properties for centuries, and since 1987 it has served as a legal sacrament for several churches in Brazil. The largest is the Uniao Do Vegetal, or UDV, which combines elements of Christianity with nature worship and claims 8,000 members.

Grob and his colleagues found that UDV members were on average healthier physiologically and psychologically than a control group. The UDV adherents also had elevated receptors for the neurotransmitter serotonin, which has been correlated with resistance to depression and other disorders. Many of the UDV members told the scientists that ayahuasca had helped them overcome alcoholism, drug addiction, and other self-destructive behaviors.

These findings emboldened UDV adherents based in New Mexico to sue the U.S. Justice Department for the right to drink their sacrament. The case dates to 1999, when federal agents seized 30 gallons of ayahuasca that the UDV group had imported from Brazil. Last August, a federal judge in Albuquerque ruled in favor of the UDV worshippers. The judge contended that the Justice Department had not shown that ayahuasca poses enough of a health risk to warrant restricting the UDV members' right to practice their religion. The Justice Department lawyers appealed, and the case is now before the 10^th Circuit Court in Denver.

Of course, even advocates of entheogens admit that they pose risks. Ayahuasca can cause cardiac irregularities and other dangerous side effects, Grob notes, when combined with amphetamines, antidepressants, cheese, red wine, and other common substances. Ayahuasca drinkers generally fast before sessions to reduce the risks of these side effects.

In the new book The Antipodes of the Mind, an in-depth study of ayahuasca visions, the Israeli psychologist Benny Shanon recalls that the tea transformed him from a "devout atheist" into someone awestruck by the wonders of nature and of human consciousness. But he warns that ayahuasca can also be "the worst of liars," leaving some users gripped by belief in ghosts, telepathy, and other occult phenomena. Similarly, in Cleansing the Doors of Perception, the eminent religious scholar Huston Smith recalls that during the Good Friday experiment, in which he participated, one subject became so agitated that he had to be injected with Thorazine. Smith nonetheless contends that entheogens can serve a spiritual purpose, if used with reverence; after all, mind-altering substances have played an inspirational role in many religions, including Hinduism and the Eleusinian cult of ancient Greece.

I have firsthand experience of the double-edged nature of entheogens, which I've taken sporadically since my late teens. There have been moments of vertiginous anxiety; one particularly bad trip in 1981 left me with unsettling flashbacks for months. But overall the pros have outweighed the cons. I usually end up feeling the way I did after my LSD sojourn last summer: existentially refreshed, with a renewed appreciation of ordinary existence.

Entheogens are far less addictive and toxic than alcohol or tobacco. Why should we continue to be denied their benefits, in religious or non-religious contexts? Risks could be minimized by making these substances available only through licensed therapists, who can screen clients for mental instability and advise them on how to make their experiences as rewarding as possible. Some people might be prescribed entheogens for a specific disorder, such as depression or alcoholism. And just as drugs such as Prozac and Viagra are prescribed not just to heal the ill but also to enhance the lives of the healthy, so might entheogens.