Could a psychedelic drug help people who are dying of cancer face their fears? Two long-awaited studies suggest that the hallucinogenic compound in magic mushrooms, psilocybin, could do just that. “They are the most rigorous double-blind placebo-controlled trials of a psychedelic drug in the past 50 years,” writes David Nutt, a pharmacologist at Imperial College London who was not involved in the work, in an editorial accompanying the papers.

Both studies, published today in the Journal of Psychopharmacology , combined a psychedelic trip with several sessions of psychotherapy. In one, at Johns Hopkins University in Baltimore, Maryland, 51 cancer patients received two doses of the drug 5 weeks apart, one relatively high and one so low that it was unlikely to have any effect. In the second study, at New York University (NYU) in New York City, 29 cancer patients randomly received either psilocybin or niacin, a compound that mimics some side effects of psilocybin—including a flushed, hot feeling—but without the hallucinogenic properties. Seven weeks later, the patients received the other compound.

Of the participants who received the high dose in the second study, 83% reported feeling significantly less depression and 58% reported less anxiety after 7 weeks. Only 14% of those who received niacin reported less anxiety and less depression. And the effect in both studies was still apparent months later. For instance, in the Johns Hopkins study, about 60% of all participants still showed normal levels of depression and anxiety after 6 months. “The findings are impressive, with good safety data and large effect sizes," says Robin Carhart-Harris, who studies psychedelic drugs at Imperial College London. "My feeling is that these studies will play a significant role in waking up the scientific and medical mainstream to the therapeutic potential of psychedelics."

Two things in particular are striking about the results, says Isabella Heuser, a psychiatrist at Charité, the University Clinic in Berlin: There seemed to be a rapid onset of the effect, and it was still measurable months later. “These are still small trials,” Heuser cautions. “But the fact that they both show very similar results is very encouraging.” Guy Goodwin, a psychiatrist at the University of Oxford in the United Kingdom, says the trials have moved the field forward. “I think they represent a kind of landmark," he says. “But they are the beginning of something, not the end or the proof of something.”

Many cancer patients develop severe depression and anxiety after their diagnosis, says Roland Griffiths, who led the John Hopkins study. These feelings can persist even when the cancer is gone. Dinah Bazer, a 69-year old woman from Brooklyn, New York, who participated in the NYU study, was diagnosed with ovarian cancer in 2010. Surgery and chemotherapy were successful but she was consumed with anxiety and fear of the cancer coming back. “It was running my life and ruining my life,” she says. “This drug saved my life.”

But patients like Bazer don’t typically have the option for such treatment today. In the 1960s, psilocybin and LSD were used to treat depression or alcoholism in numerous trials. But widespread misuse—and their association with the counter-culture—led to a political backlash. In 1970, U.S. President Richard Nixon banned the drugs and virtually all research ceased. Research started up again in the 1990s, but it has been hampered by strict regulations and methodological issues.

One of the problems facing researchers is how to ensure that participants and investigators don’t know whether they are dealing with the drug or a placebo. In the Johns Hopkins study, participants and therapists were told that patients would receive psilocybin on both occasions and that the dose could vary. But fooling participants who might be feeling the effects of a powerful mind-altering drug isn’t easy. This is particularly worrisome, because the measures of effect on depression or anxiety tend to be subjective, Goodwin says. “If they could show for instance that people go back to work or that they move around more, that would be objective evidence.”

How exactly psilocybin could lead to a decrease in anxiety and depression is unclear. Both studies found that patients who have a stronger mystical experience also showed a better outcome, whether or not they reported being religious, says Stephen Ross, who led the NYU study. Bazer, for instance, says she experienced “being bathed in God’s love” for hours after taking psilocybin. “I really had no other way to describe this incredibly powerful experience," says Bazer, who says she was and still is an atheist. “I believe this was something that happened in my brain." But whether that experience somehow catalyzes changes itself, or is just a side effect of other changes, is hard to pinpoint.

Either way, the treatment could help many patients, Ross says. The Food and Drug Administration is currently reviewing an application for a phase III trial of psilocybin, the last step before the therapy could be approved. There is good reason to be hopeful, Ross says. On Tuesday, the regulatory body gave the green light for a phase III trial of another contentious drug: using ecstasy to treat posttraumatic stress disorder.