ABSTRACT
This chapter discusses several classes of drugs. Lysergic acid diethylamide (LSD) shows cross tolerance for most of the other hallucinogens, but not for phencyclidine (PCP) or the atropine-like drugs. Only LSD and PCP are important agents of abuse, because they are readily synthesized in the U.S. and therefore widely available. Street drugs in these categories are often adulterated.
