A reader named Tharpa suggested I look at a Johns Hopkins study of mushrooms containing psilocybin, a psychoactive chemical. The results were quite positive, and a lot less scary and disturbing than many of the ayahuasca reports I'd read.
The study was first reported in 2006. Here are excerpts from the university's press release:
All of the study’s authors caution about substantial risks of taking psilocybin under conditions not appropriately supervised. “Even in this study, where we greatly controlled conditions to minimize adverse effects, about a third of subjects reported significant fear, with some also reporting transient feelings of paranoia,” says [Dr. Roland] Griffiths. “Under unmonitored conditions, it’s not hard to imagine those emotions escalating to panic and dangerous behavior.”The researchers’ message isn’t just that psilocybin can produce mystical experiences. “I had a healthy skepticism going into this,” says Griffiths, “and that finding alone was a surprise.” But, as important, he says, “is that, under very defined conditions, with careful preparation, you can safely and fairly reliably occasion what’s called a primary mystical experience that may lead to positive changes in a person. It’s an early step in what we hope will be a large body of scientific work that will ultimately help people.”...
In the study, more than 60 percent of subjects described the effects of psilocybin in ways that met criteria for a “full mystical experience” as measured by established psychological scales. One third said the experience was the single most spiritually significant of their lifetimes; and more than two-thirds rated it among their five most meaningful and spiritually significant. Griffiths says subjects liken it to the importance of the birth of their first child or the death of a parent.
Two months later, 79 percent of subjects reported moderately or greatly increased well-being or life satisfaction compared with those given a placebo at the same test session. A majority said their mood, attitudes and behaviors had changed for the better. Structured interviews with family members, friends and co-workers generally confirmed the subjects’ remarks....
Psychological tests and subjects’ own reports showed no harm to study participants, though some admitted extreme anxiety or other unpleasant effects in the hours following the psilocybin capsule. The drug has not been observed to be addictive or physically toxic in animal studies or human populations.
A follow-up stud showed that the beneficial effects lasted more than a year. Excerpts from a 2008 Hopkins press release:
Writing in the Journal of Psychopharmacology, the Johns Hopkins researchers note that most of the 36 volunteer subjects given psilocybin, under controlled conditions in a Hopkins study published in 2006, continued to say 14 months later that the experience increased their sense of well-being or life satisfaction.
"Most of the volunteers looked back on their experience up to 14 months later and rated it as the most, or one of the five most, personally meaningful and spiritually significant of their lives," says lead investigator Roland Griffiths, Ph.D. ...
"This is a truly remarkable finding," Griffiths says. "Rarely in psychological research do we see such persistently positive reports from a single event in the laboratory. This gives credence to the claims that the mystical-type experiences some people have during hallucinogen sessions may help patients suffering from cancer-related anxiety or depression and may serve as a potential treatment for drug dependence. We're eager to move ahead with that research."
Griffiths also notes that, "while some of our subjects reported strong fear or anxiety for a portion of their day-long psilocybin sessions, none reported any lingering harmful effects, and we didn't observe any clinical evidence of harm."
The research team cautions that if hallucinogens are used in less well-supervised settings, the possible fear or anxiety responses could lead to harmful behaviors.
Also relevant to this discussion is William James' experiment with nitrous oxide. His first impressions are recounted here.
In his book The Varieties of Religious Experience, James famously wrote:
I myself made some observations on ... nitrous oxide intoxication, and reported them in print. One conclusion was forced upon my mind at that time, and my impression of its truth has ever since remained unshaken. It is that our normal waking consciousness, rational consciousness as we call it, is but one special type of consciousness, whilst all about it, parted from it by the filmiest of screens, there lie potential forms of consciousness entirely different.