Neuropharmacology is the study of drugs that affect the nervous system where drugs are defined not only as agents that are foreign to the organism but include endogenous substances such as l-dopa. In the central nervous system (CNS), neuropharmacology encompasses the psychotropic drugs which alter mood and behavior, general anesthetics, analgetics, anticonvulsants, hypnotics, analeptics, and narcotics. In the peripheral nervous system, neuropharmacology includes drugs that block axonal conduction, neuromuscular blocking agents, and an extraordinary range of drugs that affect the autonomic and enteric nervous systems. Since neuropharmacology is not a specific discipline with its own technology such as neurophysiology or neurochemistry, neuropharmacologists, depending on their training, represent virtually every field of biomedical science. As long as their primary concern is with neuroactive drugs, investigators can choose to be classified as neuropharmacologists regardless of whether they are endocrinologists, immunologists, physiologists, or chemists.