Antidepressants: What They Actually Do, What the Evidence Shows, and What the Criticism Gets Right

Antidepressants are among the most prescribed medications in the world and among the most contested in popular discourse. The contest has two false poles: the pharmaceutical-promotional position ("antidepressants are effective, well-tolerated, and underused") and the antipsychiatry position ("antidepressants are no better than placebo, the serotonin hypothesis is false, and the drugs harm people"). Both are wrong in specific ways.

The Evidence on Efficacy

The largest and most methodologically rigorous meta-analysis of antidepressant efficacy was published by Cipriani et al. in The Lancet in 2018 — pooling 522 RCTs and 116,000+ participants across 21 antidepressants compared to each other and placebo.

Findings: All 21 antidepressants outperformed placebo for acute-phase treatment of major depressive disorder. Odds ratios for response (typically defined as ≥50% symptom reduction) ranged from approximately OR 1.4 to OR 2.1 against placebo. In response rate terms: roughly 40–60% of patients responded to antidepressant versus 30–40% on placebo.

The absolute difference: approximately 15–20 percentage points. Real. Not dramatic.

Irving Kirsch's critique: Kirsch's analysis of FDA trial data found that the drug-placebo difference in symptom score reduction fell below clinical significance thresholds for mild-to-moderate depression, reaching clinical significance primarily in severe cases. This is a legitimate finding. It does not mean antidepressants don't work — it means the effect is most meaningful for severe depression and less clear for mild-to-moderate.

> 📌 Cipriani et al. (2018) Lancet meta-analysis of 522 RCTs: all 21 antidepressants significantly more effective than placebo; sertraline (Zoloft) and escitalopram (Lexapro) showed favorable efficacy-tolerability profiles; agomelatine, mirtazapine, and amitriptyline showed highest efficacy; placebo response was substantial (30–40%) across all trials. [1]

The Serotonin Hypothesis

The "chemical imbalance" explanation — that depression is caused by low serotonin and antidepressants correct this deficiency — is a significant oversimplification that most of the psychiatric research community had moved away from by the early 2000s.

A 2022 umbrella review by Moncrieff et al. in Molecular Psychiatry concluded that evidence for a simple relationship between serotonin function and depression is weak. This was widely misrepresented as proof that antidepressants don't work. The serotonin hypothesis was never the mechanism — it was a flawed marketing simplification. The actual mechanisms are more complex: BDNF upregulation, hippocampal neurogenesis, synaptic remodeling, anti-inflammatory effects. None of that is serotonin balance.

Antidepressants work. The serotonin deficiency explanation for why they work was never accurate.

Withdrawal and Discontinuation

Discontinuation syndrome is underappreciated. Abrupt cessation of many SSRIs and SNRIs produces withdrawal symptoms: dizziness, electric shock sensations ("brain zaps"), flu-like symptoms, anxiety, irritability. This is not addiction — cravings and dose escalation are absent — but it is physiological dependence with withdrawal.

The practical implication: antidepressants should be tapered, not stopped abruptly, and patients should be informed of discontinuation risk before starting.

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