Though immortalized by writers such as Hunter S. Thompson, the hallucinogenic cactus peyote may not have discernible long-term consequences on the people who regularly consume it for religious sacrament, according to a recent study.

A report released on Friday by the Harvard-affiliated McLean Hospital indicates that the mescaline-containing plant leaves users psychologically unscathed and may even contribute to an increase in certain types of mental performance.

In 1994, peyote was declared legal for consumption in the rituals of the Native American Church, although it is still classified by the U.S. government as a controlled substance whose non-religious use is illegal. Members of the Church—particularly in the American Southwest and Mexico, where the plant naturally grows—ritualistically eat buttons of peyote as part of their regular campfire ceremonies.

Five years ago, the researchers from McLean—a Boston hospital specializing in mental health—set out to verify the claims of the Native American Church that the drug causes little, if any, long-term psychological damage.

For the study, Instructor in Psychiatry John H. Halpern traveled to the Southwest to spend time with members of the Navajo tribe. During his stay, Halpern consumed peyote as part of the Church’s sacrament and conducted tests on hundreds of tribe members.

The study compared the results of a basic psychological exam given to 60 Native American Church members who had used peyote over 100 times, 79 tribe members who did not use the drug, and 36 individuals with a history of alcohol abuse but little or no peyote consumption.

According to Halpern’s results, frequent peyote users did better on the cognitive exam than those who struggled with alcoholism, and even outperformed Navajos who were alcohol- and peyote-free.

The study also revealed that frequent peyote use causes no long-term psychological damage.

According to Professor of Psychiatry Emeritus Lester Grinspoon, who specializes in the effects of psychotropic drugs, a typical sacrament ceremony entails encircling a campfire and swallowing peyote buttons.

“One of the most interesting parts of the study for me, as someone who never believed in the harm of controlled hallucinogens, was that it was done at all,” said Grinspoon, who has penned several books that question the hazard of common psychotropic drugs.

Grinspoon commended the McLean team’s courage and their ability to overcome logistical obstacles. “Methodologically,” he says, “these people did really well.”

Harvard Medical School (HMS) Professor of Psychiatry Harrison Pope, the senior author of the McLean study, said he and Halpern were initially interested in exploring the psychological effects of a hallucinogen on individuals who used no other drugs. “The Navajo seemed a perfect test group,” Pope says, because church members “explicitly abstain from other drugs.”

While the outcome of the McLean study certainly means comfort for the 300,000 legal users of peyote in the United States, the results apply only to this particular drug. “One must be very careful not to generalize.” Pope cautions. “People who read this study cannot conclude that [other hallucinogens] are equally benign.”

Peyote, unlike the common street drugs LSD and PCP, derives its hallucinogenic effects from mescaline, rendering the study’s results applicable only for mescaline-based substances.

In describing the differences between a peyote-induced trip and one involving mushrooms or LSD, the study notes that the peyote high is more “sensual and perceptual.” Additionally, none of the study’s subjects experienced the “flashbacks” so common among users and former users of other hallucinogenic drugs.

Grinspoon said it was refreshing to have confirmation within the scientific community of peyote’s psychological benevolence. “I think [peyote] helps the ritual [of the Church], and the afterglow helps people sustain their abstinence [from alcohol],” Grinspoon said.

This article has been revised to reflect the following correction:

CORRECTION: May 14, 2012

An earlier version of this article mischaracterized the religious rituals of the Native American Church. In fact, vomiting and dancing are not significant elements of the Church's sacrament.