LSD - lysergic acid diethylamide is a hallucinogenic drug. LSD is commonly called 'acid'. The experience is known as a 'trip' and these trips can be good or bad. A trip can take from 20 minutes to an hour to start and usually lasts about 12 hours. Once it's started you can't stop it. And until you take a tab of acid you can't tell how strong it is or how it's going to affect you.