. >> carine mclaughlin: people ask me, "do you want to do it again?" no, i don't want to go do that again." >> cooper: it was really that bad? >> mclaughlin: oh, it was awful. the entire time, other than the very end and the very beginning, i was crying. >> cooper: carine mclaughlin is talking about the hallucinogenic experience she had here at johns hopkins university, after being given a large dose of psilocybin, the psychedelic agent in magic mushrooms, as part of an ongoing clinical trial. >> roland griffiths: we tell people that their experiences may vary, from very positive, to transcendent and lovely, to literally hell realm experiences. >> cooper: hell realm? >> griffiths: as frightening an experience as you have ever had in your life. >> cooper: that's scientist roland griffiths. for nearly two decades now, he and his colleague matthew johnson have been giving what they call "heroic doses" of psilocybin to more than 350 volunteers, many struggling with addiction, depression and anxiety. can you tell who is going to have a bad experience, who's