The researchers' study, published in the Journal of Psychopharmacology, found a single high dose of the hallucinogen psilocybin found in magic mushrooms, lasted at least a year in nearly 60 percent of the 51 participants.
Study leader Roland R. Griffiths, a professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine in Baltimore, said lasting change was found in the part of the personality known as openness -- which includes traits related to imagination, aesthetics, feelings, abstract ideas and general broad-mindedness. Changes in these traits, measured on a widely used and scientifically validated personality inventory, were larger in magnitude than changes typically observed in healthy adults over decades of life experiences, Griffiths said.
Researchers say after age 30, personality doesn't usually change significantly.
"Normally, if anything, openness tends to decrease as people get older," Griffiths said in a statement.
Nearly all of the participants in the study considered themselves spiritually active, more than half had postgraduate degrees and the sessions with the otherwise illegal hallucinogen were closely monitored and volunteers were considered to be psychologically healthy, the researchers said.
"We don't know whether the findings can be generalized to the larger population," Griffiths said.
However, Griffiths noted some study participants reported strong fear or anxiety for a portion of their daylong psilocybin sessions. Although none reported any lingering harmful effects, if hallucinogens are used in less well-supervised settings, the possible fear or anxiety responses could lead to harmful behaviors.