In a massive study published in the Journal of Psychopharmacology, scientists at the Norwegian University for Science and Technology at Trondheim concluded that there is no link between the use of LSD and psilocybin (the active ingredient in magic mushrooms) and mental-health problems. The study selected 135,000 participants at random—including 19,000 who had used psychedelic drugs—and found no evidence linking such drugs to the onset of mental disorders.

"Over 30 million U.S. adults have tried psychedelics and there just is not much evidence of health problems," the author and clinical psychologist Pål-Ørjan Johansen said.

Johanesen was careful to acknowledge that users of psychedelic drugs are not immune to bad trips, and are as susceptible as anyone else to mental-health issues. But his findings negate a common perception that drugs like LSD put users directly in danger—a justification used in criminalization.

"This study assures us that there were not widespread 'acid casualties' in the 1960s,” Charles Grob, a pediatric psychiatrist at UCLA, told Nature.

The study's publication arrives at a time when interest in psychedelic drugs—or at least their scientific usefulness—is surging. In The New Yorker, the journalist Michael Pollan profiled scientists at New York University whose experiments with administering psilocybin have had largely positive results—particularly among participants stricken with terminal cancer. And in the U.K., 12 patients suffering from clinical depression will take magic mushrooms in a study next year at London's Imperial College.

Most psychedelic drugs—including LSD and psilocybin—have been illegal in the United States since 1970, the year President Richard Nixon signed the Controlled Substances Act. The legislation classified LSD and mushrooms under Schedule 1, prohibiting not only their consumption and sale but also their use in medicine. Research into the therapeutic benefits of psychedelic drugs largely froze after decades of frenetic scientific investigation.

Despite a revival in scientific interest, a legislative reconsideration of LSD and mushrooms is not yet on the table, and may not be desirable. But a renewed enthusiasm for examining psychedelic substances hints, as with the gradual relaxing of marijuana laws across the country, at a more humane, rational approach to the criminalization of drugs.