pi. n. One class of psychotropic drugs usually prescribed for the treatment of depression. Although the exact mechanisms of action remain unclear, antidepressants primarily work by altering levels of various neurotransmitters (for example, serotonin) available at receptor sites in the brain. At least four distinct classes are in current clinical use: ssris (selective serotonin-reuptake inhibitors), mixed-function (or dual-action agents), tricyclic acids (TCAs), and monoamine oxidase inhibitors (MAOIs). For bipolar mood disorders several of these classes may be used to stabilize mood.