A bad trip (also known as challenging experiences, acute intoxication from hallucinogens, psychedelic crisis, or emergence phenomenon) is an acute adverse psychological reaction to the effects of psychoactive substances, namely psychedelics. There is no clear definition of what constitutes a bad trip. Additionally, knowledge on the cause of bad trips and who may be vulnerable to such experiences are limited. Existing studies report that possible adverse reactions include anxiety, panic, depersonalization, ego dissolution, paranoia, as well as physiological symptoms such as dizziness and heart palpitations. However, most studies indicate that the set and setting of substance use influence how people respond.
Bad trips can be exacerbated by the inexperience or irresponsibility of the user or the lack of proper preparation and environment for the trip, and are often reflective of unresolved psychological tensions triggered during the course of the experience. In clinical research settings, precautions including the screening and preparation of participants, the training of the session monitors who will be present during the experience, and the selection of appropriate physical setting can minimize the likelihood of psychological distress. Researchers have suggested that the presence of professional "trip sitters" (i.e., session monitors) may significantly reduce the negative experiences associated with a bad trip. In most cases in which anxiety arises during a supervised psychedelic experience, reassurance from the session monitor is adequate to resolve it; however, if distress becomes intense it can be treated pharmacologically, for example with the benzodiazepine diazepam.