Psychopharmacology (from Greek ψῡχή, psȳkhē, "breath, life, soul"; φάρμακον, pharmakon, "drug"; and -λογία, -logia) is the scientific study of the effects drugs have on mood, sensation, thinking, and behavior. It is distinguished from neuropsychopharmacology, which emphasizes the correlation between drug-induced changes in the functioning of cells in the nervous system and changes in consciousness and behavior. The field of psychopharmacology studies a wide range of substances with various types of psychoactive properties, focusing primarily on the chemical interactions with the brain. The term "psychopharmacology" was probably first coined by David Macht in 1920. Psychoactive drugs interact with particular target sites or receptors found in the nervous system to induce widespread changes in physiological or psychological functions. The specific interaction between drugs and their receptors is referred to as "drug action", and the widespread changes in physiological or psychological function is referred to as "drug effect". These drugs may originate from natural sources such as plants and animals, or from artificial sources such as chemical synthesis in the laboratory.

The dawn of contemporary psychopharmacology marked the beginning of the use of psychiatric drugs to treat psychological illnesses. It brought with it the use of opiates and barbiturates for the management of acute behavioral issues in patients. In the early stages, psychopharmacology was primarily used for sedation. Then with the 1950s came the establishment of chlorpromazine for psychoses, lithium carbonate for mania, and then in rapid succession, the development of tricyclic antidepressants, monoamine oxidase inhibitors, benzodiazepines, among other antipsychotics and antidepressants. A defining feature of this era includes an evolution of research methods, with the establishment of placebo-controlled, double blind studies, and the development of methods for analyzing blood levels with respect to clinical outcome and increased sophistication in clinical trials. The early 1960s revealed a revolutionary model by Julius Axelrod describing nerve signals and synaptic transmission, which was followed by a drastic increase of biochemical brain research into the effects of psychotropic agents on brain chemistry.[3] After the 1960s, the field of psychiatry shifted to incorporate the indications for and efficacy of pharmacological treatments, and began to focus on the use and toxicities of these medications.The 1970s and 1980s were further marked by a better understanding of the synaptic aspects of the action mechanisms of drugs. However, the model has its critics, too – notably Joanna Moncrieff and the Critical Psychiatry Network.