The hydrochloride salt of the tricyclic dibenzocycloheptadiene amitriptyline with antidepressant and antinociceptive activities. Amitriptyline inhibits the re-uptake of norepinephrine and serotonin by the presynaptic neuronal membrane in the central nervous system (CNS), thereby increasing the synaptic concentration of norepinephrine and serotonin. Due to constant stimulation to these receptors, amitriptyline may produce a downregulation of adrenergic and serotonin receptors, which may contribute to the antidepressant activity. In the CNS the antinociceptive activity of this agent may involve high affinity binding to and inhibition of N-methyl-D-aspartate (NMDA) receptors and/or the enhancement of the action of serotonin at the spinal terminals of an opioid-mediated intrinsic analgesia system. OR A drug that is used to treat depression and may be given to treat anxiety, sleep disorders, and pain. It is also being studied in an oral or gel form in the treatment of nerve pain caused by chemotherapy. Amitriptyline hydrochloride is a type of tricyclic antidepressant. Also called amitriptyline.