Psychoactive drugs are ingested chemicals that cross the blood-brain barrier and produce a change in brain neurotransmitter function resulting in altered mood or behavior. These compounds can be used therapeutically, as is the case for antipsychotic, antiseizure, and antidepressant medications. These compounds can also be used recreationally, as is the case for traditional “drugs of abuse” such as cocaine, heroin, or marijuana. Regardless of the intent of the user, psychoactive drugs can produce robust changes in lifestyle, health, and behavior. The focus of this entry will be on psychoactive drugs with potential for abuse. Specifically, the behavioral pharmacology, use of, dependence on, and abuse of these drugs will be discussed.