Some of the adverse effects of TCAs are predictable from their
pharmacodynamic actions. These include (1) excessive sedation, lassitude,
fatigue, and, occasionally, confusion; (2) sympathomimetic effects,
including tachycardia, agitation, sweating, and insomnia; (3) antimuscarinic
effects (especially amitriptyline); (4) orthostatic hypotension,
electrocardiographic abnormalities, and cardiomyopathies; (5) tremor
and paresthesias; and (6) weight gain. Overdosage with tricyclics
is extremely hazardous, and the ingestion of as little as a 2-week
supply has been lethal. Manifestations of overdose include (1) agitation,
delirium, neuromuscular irritability, convulsions, and coma; (2)
respiratory depression and circulatory collapse; (3) hyperpyrexia;
and (4) cardiac conduction defects and severe arrhythmias. The “3
Cs”—coma, convulsions, and cardiotoxicity—are characteristic.