Tolerance to LSD's hallucinatory and physical effects develops rapidly, making larger amounts of the drug necessary to produce the same effects. Often, within a few days of consecutive daily doses, no amount of the drug will produce the desired effects. After several days of abstinence, however, both the hallucinatory effects and the effects on blood pressure and reflexes are again felt. A person who
has built up tolerance to LSD will also be resistant to the effects of the other, less potent hallucinogens, such as psilocybin and mescaline. This phenomenon is called cross-tolerance.

There is no physical dependence on LSD after continuous use, for there are no withdrawal symptoms after the drug is discontinued.

Some regular LSD users become psychologically dependent on the drug, and the need to keep taking it becomes a compulsion. They represent a small minority of LSD users, however, and in street language are called "acid heads" or "acid
freaks."