LSD

Definition: peripherally, a serotonin antagonist; 1–2 mcg or less per kg induces hallucinatory states; its use may precipitate psychoses; it was formerly occasionally used in the treatment of long-term alcoholism and psychotic disorders. Some people take this drug to go into a different state of mind. Many call it tripping, but when you take LSD it is said to take "chunks out of your brain."
This is not to be messed around with. LSD can have long term affects on you, some people are said to go on life long trips that they can never get out because the drug was to effective on their brain.