The drug’s effects would last up to 10 hours, after which the patient would sleep on a couch in the office, attended at all times by the therapist or an assistant. “I told them that each session would be right here, in a safe environment, and I am part of it,’” Dr. Gasser said. “I said, ‘I can’t guarantee you won’t have intense distress, but I can tell you that if you do, it will pass.’ ”

And so they did — and indeed it passed, though not always easily. Many wept, most squirmed; one 67-year-old man said he met his long-dead, estranged father somewhere out in the cosmos, nodding in approval.

All talked for periods with Dr. Gasser, who acted as an anchor in the storm and a fellow explorer, tracking the sources of those emotions. In the jargon of the profession, the therapy was patient-centered, open-ended and “integrative,” in that it focused on current habits of thought as well as on long-ago childhood scenes.

“I had what you would call a mystical experience, I guess, lasting for some time, and the major part was pure distress at all these memories I had successfully forgotten for decades,” Peter said. “These painful feelings, regrets, this fear of death. I remember feeling very cold for a long time. I was shivering, even though I was sweating. It was a mental coldness, I think, a memory of neglect.”

He was also doing something with those sensations, something he had almost never done before. He was talking about them. “It surprised me,” Peter said. “I didn’t know I was talking away until Dr. Gasser made me notice.”

After about two months of weekly therapy, the eight participants who received full doses of LSD improved by about 20 percent on standard measures of anxiety, and the four subjects who took a much weaker dose got worse. (After the trial, those patients were allowed to “cross over” and try the full dose.) Those findings held up for a year in those who have survived.

The trial was far too small to be conclusive, said Dr. Gasser, whose co-authors include Dr. Doblin, Dominique Holstein of UniversityHospital Zurich and Rudolf Brenneisen of the University of Bern. But the researchers see the results as a beginning. The drug caused no serious side effects, other than temporary — and therapeutically valuable — periods of distress.