A bad trip is a profoundly unpleasant experience using a psychotropic drug such as LSD or psilocybin, caused by one or more of the common undesired effects of the drug:

• Panic reaction
• Amplification of unconscious fears
• Self-aggression
• Suicidal or homicidal ideation
• Fear of going insane or of the inability to return to normal
• Perception of rapid aging of self or others
• Profound depression

The effects of psychotropic drugs vary widely from one individual to the next. Psychosis is exacerbated in individuals already suffering from this condition. Sometimes individuals under the influence of such drugs have forgotten that they have taken them, and believe that the wildly distorted world the perceive is real and will be with them indefinitely. In extreme cases, hospitalization is required, though the value of this practice is disputed by proponents of recreational use of psychotropic compounds.

Medical treatment consists of supportive therapy and minimization of external stimuli. In some cases, sedation is used when necessary to control self-destructive behavior, or when hyperthermia occurs. Valium is the most frequently used sedative for such treatment.

Timothy Leary taught that a bad trip is a result of bad set and setting, and advised that users of hallucinogens be sure that they are comfortable before taking the drugs. Leary claimed that the frequency of bad trips, although highly exaggerated with anecdotes and fabrications in the popular press, was actually about 1 in 1000. He taught that a simple temporary fix to a bad trip is sugar (i.e. candy, oranges), since bad trips are often the result of people forgetting to eat and experiencing hyperawareness of low blood sugar.