A bad trip 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. According to the California Legislature's 1969 substance abuse guide, the term "freak-out" was used to refer to a bad trip during the 1960s.