In 2016, a study was done at Johns Hopkins by Roland Griffiths and others, in which 1993 individuals completed an online survey about their single most psychologically difficult or challenging experience (worst "bad trip") after consuming psilocybin mushrooms. 11% put self or others at risk of physical harm. 2.6% behaved in a physically aggressive or violent manner and 2.7% received medical help. Of those whose experience occurred >1 year before, 7.6% sought treatment for enduring psychological symptoms. Three cases appeared associated with onset of enduring psychotic symptoms and three cases with attempted suicide. Difficulty of experience was positively associated with dose. Despite difficulties, 84% endorsed benefiting from the experience. It was concluded that the incidence of risky behavior or enduring psychological distress is extremely low when psilocybin is given in laboratory studies to screened, prepared, and supported participants. Safeguards against these risks in the clinical trials at Johns Hopkins include the exclusion of volunteers with personal or family history of psychotic disorders or other severe psychiatric disorders.