A substance that exerts an effect on a biological system. For the most part, drugs are either derived from living systems (plants for instance) or synthesized in the laboratory. Thousands of different types of drugs exist, which are used for a wide array of purposes ranging from therapeutic to recreational. Drugs that have an effect on the brain and/or behaviour are often termed psychoactive, and are studied in the field of PSYCHOPHARMACOLOGY. Drug effects refer to the changes in the normal biological state that the drug causes.
For PSYCHOACTIVE drugs, these changes are usually alterations in behaviour, perception, or subjective feelings. Drugs can, and usually do, have multiple effects; for example, MORPHINE lessens PAIN perception, but also depresses respiratory rate. COCAINE induces EUPHORIA, but also causes changes in heart rate and blood pressure. Drug effects are the result of drug actions, that is, the mechanism by which the drug causes behavioural or physiological effects. Drugs may have multiple actions as well. Although we mostly think of drugs as EXOGENOUS agents, compounds that occur naturally in the body or brain are also synthesized and used as drugs, such as INSULIN, MELATONIN, TRYPTOPHAN, L-DOPA, ADRENALINE and CORTISOL, to name just a few.
ANN E.KELLEY
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