[ABSTRACT] The antidepressant drugs are being commonly used in the treatment of chronic pain since forty years ago. In this sense, the most used are the classical tricyclic antidepressants (TAD) and the monoaminooxidase inhibitors (IMAO). The analgesic action of the TAD seems to be independent from the antidepressive action, despite of the fact that most of the chronic pain symptoms involve an associated depressive component. In fact, these agents act on the pain at low doses, in a temporal rang