Antimuscarinic and other receptor-blocking properties of antidepressants.

Tricyclic antidepressants (for example, amitriptyline) and other types of antidepressants (for example, amoxapine and maprotiline) are competitive antagonists of muscarinic acetylcholine receptors, the predominant class of acetylcholine receptors in the brain. Some evidence suggests that this muscarinic receptor blockade in brain alleviates depression. However, all tricyclic antidepressants appear to be equally effective in treating depression despite having differences in their antimuscarinic potencies while having similar ranges of therapeutic blood levels. It is more likely that the antimuscarinic potency of antidepressants is related mainly to the frequency with which they cause such symptoms as blurred vision, dry mouth, and urinary retention. Information on the antimuscarinic potency and other receptor-blocking potencies of antidepressant agents can be helpful in minimizing or avoiding certain side effects when these drugs are given to patients.