Pharmacology · Selective serotonin reuptake inhibitors (SSRIs)
Citalopram !
An SSRI for depression, the racemic parent of escitalopram. It prolongs the QT interval in a dose-dependent way, so heart risk factors matter.
Updated 2026-11-01
The figure shows S-citalopram (escitalopram), the active half of citalopram, at the central site of a thermostabilised human SERT (ts3).
Mechanism of action
Citalopram is a racemic mixture; its S-enantiomer (escitalopram) blocks the serotonin transporter and gives the antidepressant effect. The drug causes dose-dependent QTc prolongation, which sets its upper dose limit.
- The S-enantiomer of citalopram binds the serotonin transporter
- Serotonin reuptake is blocked
- Serotonin signalling increases and mood improves over weeks
- At higher exposure the QTc interval lengthens
Pharmacokinetics
- Absorption
- By mouth
- Metabolism
- Mainly in the liver; CYP2C19 poor metabolisers and CYP2C19 inhibitors raise exposure
- Half-life
- Long, allowing steady levels; doubled in liver impairment and longer in older adults
Indications
- Major depressive disorder in adults
Adverse effects
Common
- Ejaculation disorder, mainly delayed ejaculation
- Nausea
- Somnolence or insomnia, fatigue
- Increased sweating
Contraindications
- MAO inhibitors, including linezolid and intravenous methylene blue, or within 14 days of stopping an MAOI
- Pimozide (QT prolongation)
- Hypersensitivity to citalopram
- Avoided in congenital long QT, bradycardia, low potassium or magnesium, recent myocardial infarction, uncompensated heart failure and with other QT-prolonging drugs
Key interactions
- Cimetidine or other CYP2C19 inhibitors
- Higher citalopram levels and more QT risk
- Class IA or III antiarrhythmics, some antipsychotics and antibiotics
- Additive QT prolongation
- MAO inhibitors and other serotonergic drugs
- Serotonin syndrome
- NSAIDs, aspirin, warfarin
- Higher bleeding risk
What is monitored
- Potassium and magnesium at baseline in people at risk of electrolyte disturbances
- ECG in people with heart disease or other QT risk factors
- Mood and suicidal thoughts
- Sodium in older adults
Administration and safety
- Given by mouth
- Low potassium or magnesium is corrected before starting
- Not combined with escitalopram (same active molecule)
Nursing care
- Ask about palpitations, fainting and heart disease, and review the medicine list for QT-prolonging drugs
- Report dizziness, palpitations or syncope at once
- Assess suicidal thoughts early in treatment and after dose changes
- Teach that abrupt stopping can cause a discontinuation syndrome
Pregnancy and breastfeeding
Used in pregnancy after weighing risks and benefits; SSRI exposure late in pregnancy is linked to neonatal adaptation problems and persistent pulmonary hypertension.
Test yourself
Think of the answer, then tap the question to see it.
Which SSRI is best known for dose-dependent QT prolongation?
Citalopram, which is why the label sets a dose ceiling and advises caution with heart disease and electrolyte problems.
Which electrolytes are corrected before starting citalopram in a person at risk?
Potassium and magnesium, because low levels increase the risk of QT prolongation and arrhythmia.
Why does cimetidine increase the risk of citalopram?
Cimetidine inhibits CYP2C19, so citalopram levels rise and the QT interval lengthens more.
Related drugs
← Back to the class: Selective serotonin reuptake inhibitors (SSRIs)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - CITALOPRAM capsule (DailyMed (U.S. National Library of Medicine), 2026); Citalopram: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.