Citalopram and escitalopram are the same drug, almost. The "almost" is the chirality, and the chirality is the whole story.
- Class
- SSRI
- Mechanism
- Pure SERT blockade — most selective SSRIs
- Typical dose
- Escitalopram 10-20 mg; citalopram 20-40 mg (max 40 in adults, 20 in >60 due to QTc)
- Half-life
- Both ~30 hours
- FDA indications
- Escitalopram: MDD, GAD. Citalopram: MDD. Off-label for many anxiety indications.
- Key adverse effects
- Generally well-tolerated; sexual dysfunction, GI early, mild sedation, QTc prolongation (dose-dependent)
Black box: Suicidal thinking/behavior in pediatric and young adult patients
Escitalopram is the S-enantiomer of citalopram — typically considered cleaner with fewer drug interactions. FDA cautions on citalopram >40 mg (QTc) and >20 mg in adults >60. Escitalopram has less stringent dose cap.
Citalopram — Celexa — is a racemic mixture. That means the bottle contains equal parts of two mirror-image molecules, the S-enantiomer and the R-enantiomer. The S-enantiomer does most of the SERT inhibition. The R-enantiomer contributes little to the antidepressant effect but contributes more than its share to the QTc-prolonging effect. Escitalopram — Lexapro — is the pure S-enantiomer. Same mechanism. Cleaner profile.
Escitalopram and citalopram are the cleanest SSRIs pharmacologically — citalopram is a racemate, escitalopram its active S-enantiomer — with the QTc concern as the defining clinical caveat.
Mechanism note: The clinical decision between them is mostly QTc margin and dosing ceiling — escitalopram has the wider safety window and is the more common first-line choice.
If the story stopped there, the choice would be simple. The story does not stop there.
In 2011 the FDA issued a safety communication on citalopram. The drug, at higher doses, prolongs QTc enough to raise the risk of torsades in vulnerable patients. The agency capped citalopram at 40 milligrams per day in adults under 60, and at 20 milligrams per day in adults 60 and older or with hepatic impairment. The cap was contentious — many clinicians felt the dose-response data was overstated — but the labeling stuck. Citalopram now lives with a meaningful dose ceiling that did not exist before. Escitalopram has a less stringent cap, typically 20 milligrams in adults, because the R-enantiomer is removed and the QTc effect is smaller.
For most patients today, escitalopram is the cleaner choice. The drug interaction profile is more favorable. The pharmacology is simpler. The dose ceiling is less constraining. The generic is widely available, and cost is no longer the differentiator it once was. Patients who do well on citalopram historically don't need to switch, but new starts often default to escitalopram.
Side effects are typical SSRI — GI early, sexual dysfunction at therapeutic doses, modest weight effects over time, occasional sweating. The class effects are the class effects. The QTc is the distinguishing concern for citalopram.
Dosing: escitalopram start 5 to 10 milligrams, target 10 to 20. Citalopram start 10 to 20 milligrams, target 20 to 40 (with the dose cap above). Both are once-daily. Both have a half-life around 30 hours that allows smooth steady-state.
- Cost
- Both generic, ~$5-15/month. Brand Lexapro/Celexa essentially unused.
- Generic status
- Citalopram generic since 2004; escitalopram since 2012.
- Formulary typical
- Tier 1 generics on all formularies. No PA.
- Access friction
- Minimal. Citalopram QTc dose cap (40 mg / 20 mg in elderly) sometimes flagged by pharmacy review.
Prescriber tip: Escitalopram has slight edge for tolerability; cost difference is now negligible. For elderly, escitalopram avoids the citalopram dose-cap conversation entirely.
The deeper lesson is that small molecular differences can matter. Chirality is not a footnote in pharmacology; it can determine whether one form of a drug is a clean tool and the other carries a cardiac signal. Keep this story in mind for the next time you see "racemic mixture" in a drug's history — there's often a sharper version waiting one purification step away.