Which feature best distinguishes tricyclic antidepressants (TCAs) from selective serotonin reuptake inhibitors (SSRIs) in terms of their adverse effect profile?

Explanation

## Distinguishing Feature: Anticholinergic Effects ### TCA vs SSRI Adverse Effect Profiles Tricyclic antidepressants possess a broad pharmacological profile that includes blockade of muscarinic cholinergic receptors, a property that SSRIs lack. This fundamental structural and pharmacological difference produces a distinct adverse effect signature. | Feature | TCAs | SSRIs | |---------|------|-------| | **Anticholinergic effects** | Prominent (dry mouth, urinary retention, constipation, blurred vision, tachycardia) | Minimal to absent | | **Cardiac conduction** | QT prolongation, arrhythmias (high-dose toxicity) | Rare, minimal cardiac effects | | **Orthostatic hypotension** | Marked (α-adrenergic blockade) | Mild | | **SIADH/Hyponatremia** | Rare | Common (10–15% incidence) | | **Sexual dysfunction** | Less common than SSRIs | Very common (40–60%) | | **Activation/Insomnia** | Sedation (tertiary amines) or activation (secondary amines) | Activation common early | | **Lethal toxicity in overdose** | High (narrow therapeutic index) | Low (wide therapeutic index) | **Key Point:** Anticholinergic effects are the hallmark adverse effect profile that clinically distinguishes TCAs from SSRIs. This is why TCAs are contraindicated in patients with glaucoma, benign prostatic hyperplasia, or cardiac conduction abnormalities. **Clinical Pearl:** The anticholinergic burden of TCAs limits their use in elderly patients, who are already at high risk for cognitive impairment, falls, and urinary retention. SSRIs are therefore preferred first-line agents in this population. **High-Yield:** While both drug classes cause sexual dysfunction, the *mechanism* differs: TCAs cause it via anticholinergic effects and α-blockade; SSRIs cause it via serotonergic inhibition of nitric oxide and dopamine in the sexual response pathway. [cite:KD Tripathi 8e Ch 12]