The important point here is that we found the sweet spot where we can optimize the positive persistent effects and avoid some of the fear and anxiety that can occur and can be quite disruptive,” says lead author Roland Griffiths, professor of behavioral biology at Hopkins. Giffiths’ study involved 18 healthy adults, average age 46, who participated in five eight-hour drug sessions with either psilocybin — at varying doses — or placebo. Nearly all the volunteers were college graduates and 78% participated regularly in religious activities; all were interested in spiritual experience. Fourteen months after participating in the study, 94% of those who received the drug said the experiment was one of the top five most meaningful experiences of their lives; 39% said it was the single most meaningful experience.