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Selective serotonin reuptake inhibitor (SSRI)

Citalopram

Citalopram is a selective serotonin reuptake inhibitor (SSRI) antidepressant used primarily to treat major depressive disorder. It is one of the most selective SSRIs with minimal effects on norepinephrine or dopamine reuptake. The most clinically important consideration is its dose-dependent QT interval prolongation, which limits maximum dosing.

Practice questionsHigh-yield facts
Drug classSelective serotonin reuptake inhibitor (SSRI)
MechanismBlocks presynaptic serotonin reuptake transporter, increasing synaptic serotonin
Main usesMajor depressive disorder, generalized anxiety disorder
Key adverse effectDose-dependent QT interval prolongation
6 min readFor medical studentsUpdated 2026-10-14

Mechanism of action

Citalopram selectively inhibits the presynaptic serotonin reuptake transporter (SERT), blocking the reabsorption of serotonin from the synaptic cleft back into the presynaptic neuron. This results in increased availability of serotonin at postsynaptic receptors in the central nervous system.

The enhanced serotonergic neurotransmission is thought to mediate the antidepressant and anxiolytic effects, though the precise mechanism by which increased serotonin alleviates depression remains incompletely understood. The therapeutic effect typically requires 2-4 weeks of continuous treatment, suggesting that downstream adaptive changes in receptor sensitivity and neuroplasticity contribute to clinical improvement.

Citalopram is highly selective for SERT with minimal affinity for norepinephrine or dopamine transporters, and negligible activity at muscarinic, histaminergic, or alpha-adrenergic receptors. This selectivity profile results in fewer anticholinergic and sedative side effects compared to older tricyclic antidepressants.

High-yield for exams
  • Citalopram causes dose-dependent QT prolongation; maximum dose 40 mg (20 mg if age >60 or hepatic impairment)
  • SSRI mechanism: blocks presynaptic serotonin reuptake transporter (SERT), increasing synaptic serotonin
  • Black box warning: increased suicidal thoughts in patients <25 years during initial treatment
  • Allow 14-day washout between MAOIs and citalopram to prevent serotonin syndrome
  • Serotonin syndrome triad: mental status changes, autonomic instability, neuromuscular excitation
  • SSRIs increase bleeding risk by depleting platelet serotonin; caution with NSAIDs and anticoagulants
  • Therapeutic effect requires 2-4 weeks; premature discontinuation is common cause of treatment failure
  • Abrupt discontinuation causes withdrawal syndrome; always taper over several weeks

Indications

FDA-approved indication:

  • Major depressive disorder (MDD)

Common off-label uses:

  • Generalized anxiety disorder
  • Panic disorder
  • Social anxiety disorder
  • Obsessive-compulsive disorder
  • Post-traumatic stress disorder
  • Premenstrual dysphoric disorder

Citalopram is considered a first-line pharmacological treatment for major depressive disorder. While only FDA-approved for depression, it demonstrates efficacy across various anxiety disorders and is frequently prescribed for these conditions. The choice among SSRIs often depends on side effect profile, drug interactions, and patient-specific factors rather than efficacy differences, as most SSRIs show comparable effectiveness for depression and anxiety.

Pharmacokinetics

Absorption: Well absorbed orally with bioavailability of approximately 80%. Peak plasma concentrations occur 2-4 hours after administration. Food does not significantly affect absorption.

Distribution: Volume of distribution is approximately 12 L/kg. Protein binding is relatively low at about 80%.

Metabolism: Extensively metabolized in the liver, primarily by CYP3A4 and CYP2C19 enzymes. The main metabolites are demethylcitalopram and didemethylcitalopram, which are less potent than the parent compound. Genetic polymorphisms in CYP2C19 can affect metabolism, with poor metabolizers achieving higher plasma concentrations.

Elimination: Elimination half-life is approximately 35 hours, allowing once-daily dosing. About 10% is excreted unchanged in urine. Steady-state concentrations are reached in approximately one week.

Special populations: Elderly patients and those with hepatic impairment show reduced clearance and may require dose adjustment. Renal impairment has minimal effect on pharmacokinetics.

Adverse effects

Common adverse effects

  • Gastrointestinal: Nausea, dry mouth, diarrhea, constipation (usually transient)
  • Central nervous system: Insomnia or somnolence, dizziness, fatigue
  • Sexual dysfunction: Delayed ejaculation, decreased libido, anorgasmia (affects 30-40% of patients)
  • Other: Sweating, tremor, weight changes

Serious adverse effects

QT interval prolongation: Citalopram causes dose-dependent QT prolongation through inhibition of cardiac potassium channels. Maximum recommended dose is 40 mg daily (20 mg in patients over 60 years, those with hepatic impairment, or CYP2C19 poor metabolizers). Avoid in patients with congenital long QT syndrome, and use caution with concurrent QT-prolonging medications or electrolyte disturbances.

Serotonin syndrome: Life-threatening condition resulting from excess serotonergic activity. Presents with mental status changes, autonomic instability (hyperthermia, tachycardia, labile blood pressure), and neuromuscular excitation (hyperreflexia, clonus, rigidity). Most commonly occurs with concomitant use of other serotonergic agents.

Bleeding risk: SSRIs impair platelet aggregation by depleting intraplatelet serotonin. Increased risk of gastrointestinal bleeding, particularly when combined with NSAIDs, aspirin, or anticoagulants.

Hyponatremia: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) can occur, especially in elderly patients and those on diuretics. Monitor sodium levels in high-risk patients.

Activation and suicidality: Black box warning for increased suicidal thinking and behavior in children, adolescents, and young adults (under 25 years) during initial treatment. Close monitoring is essential in the first few weeks, especially when starting or changing doses.

Discontinuation syndrome: Abrupt cessation can cause dizziness, nausea, headache, irritability, and sensory disturbances. Taper gradually over several weeks to minimize symptoms.

Contraindications and warnings

Absolute contraindications:

  • Concurrent use with monoamine oxidase inhibitors (MAOIs) or within 14 days of discontinuing an MAOI
  • Concurrent use with pimozide (increased risk of QT prolongation)
  • Known hypersensitivity to citalopram
  • Congenital long QT syndrome

Warnings and precautions:

Pregnancy and lactation: Pregnancy category C. Third-trimester exposure is associated with neonatal complications including persistent pulmonary hypertension of the newborn (PPHN), respiratory distress, and neonatal adaptation syndrome. Weigh risks and benefits carefully. Citalopram is excreted in breast milk; monitor infants for adverse effects if breastfeeding.

Bipolar disorder: Can precipitate manic episodes in patients with undiagnosed bipolar disorder. Screen for personal or family history of mania before initiating treatment.

Seizure disorder: Use cautiously in patients with seizure disorders, though SSRIs have relatively low seizure risk.

Angle-closure glaucoma: SSRIs can cause mydriasis and precipitate angle-closure glaucoma in susceptible individuals.

Hepatic and renal impairment: Reduce maximum dose to 20 mg daily in patients with hepatic impairment. No adjustment needed for renal impairment.

Drug interactions

MAOIs: Contraindicated due to risk of fatal serotonin syndrome. Allow at least 14 days between discontinuing an MAOI and starting citalopram, and at least 14 days after stopping citalopram before starting an MAOI.

Serotonergic drugs: Increased risk of serotonin syndrome when combined with other serotonergic agents including other SSRIs, SNRIs, triptans, tramadol, St. John's wort, tryptophan, amphetamines, and linezolid. Use caution and monitor closely.

QT-prolonging drugs: Additive QT prolongation with antiarrhythmics (amiodarone, sotalol), antipsychotics (ziprasidone, haloperidol), antibiotics (macrolides, fluoroquinolones), and others. Avoid combination when possible; if necessary, monitor ECG.

CYP2C19 inhibitors: Omeprazole, cimetidine, and other CYP2C19 inhibitors can increase citalopram levels. Maximum dose should not exceed 20 mg daily when combined with these agents.

Anticoagulants and antiplatelet agents: Increased bleeding risk when combined with warfarin, aspirin, NSAIDs, or other anticoagulants due to impaired platelet function.

Drugs affecting electrolytes: Diuretics, laxatives, and other medications causing hypokalemia or hypomagnesemia increase QT prolongation risk.

Alcohol: While no pharmacokinetic interaction exists, concurrent alcohol use is not recommended due to additive CNS depression.

Clinical pearls

  • Citalopram is often considered one of the better-tolerated SSRIs due to its selectivity and relatively favorable side effect profile, but QT prolongation limits maximum dosing.
  • The 40 mg maximum dose restriction was implemented after post-marketing data revealed dose-dependent QT prolongation. Do not exceed 20 mg in patients over 60, those with hepatic impairment, or CYP2C19 poor metabolizers.
  • Obtain a baseline ECG in patients with cardiac risk factors, electrolyte disturbances, or concurrent use of other QT-prolonging medications. Maintain potassium and magnesium within normal limits.
  • Sexual dysfunction is a common reason for treatment discontinuation. Discuss this potential side effect proactively, as patients may be reluctant to report it. Management strategies include dose reduction, drug holiday (not recommended due to discontinuation symptoms), or switching to an alternative antidepressant with lower sexual dysfunction rates.
  • When switching between SSRIs or to/from an SSRI to another antidepressant class, consider washout periods and cross-tapering strategies based on half-lives and interaction potential.
  • Escitalopram, the S-enantiomer of racemic citalopram, is often preferred over citalopram because it achieves therapeutic effect at lower doses (10-20 mg vs 20-40 mg) without the QT prolongation concerns at therapeutic doses.
  • Response to antidepressant therapy should be assessed after 4-6 weeks at therapeutic dose. If inadequate response, consider dose optimization, switching agents, or augmentation strategies.
  • Genetic testing for CYP2C19 polymorphisms may help identify poor metabolizers who are at higher risk for adverse effects and require dose reduction.
  • Treatment duration for a first major depressive episode should be at least 6-12 months after achieving remission. Patients with recurrent depression may require indefinite maintenance therapy.

Practice questions

1. A 68-year-old woman with major depressive disorder has been taking citalopram 40 mg daily for 3 months with good symptom control. She presents for routine follow-up. Her medical history includes hypertension and hypothyroidism. ECG shows QTc interval of 485 ms (normal <460 ms in women). Which of the following is the most appropriate next step?

Answer: B. The maximum recommended dose of citalopram in patients over 60 years is 20 mg daily due to dose-dependent QT prolongation. This patient's prolonged QTc confirms the cardiac risk. Reducing to 20 mg daily addresses the safety concern while maintaining treatment. Simply continuing the current dose ignores a significant safety issue. While switching to another SSRI is reasonable, dose reduction is more direct and maintains a medication that is working. Propranolol does not reverse drug-induced QT prolongation, and abrupt discontinuation should be avoided due to withdrawal symptoms.

2. A 22-year-old man being treated with citalopram 20 mg daily for depression presents to the emergency department with agitation, confusion, fever of 39.2°C (102.6°F), profuse sweating, and muscle rigidity. He started taking tramadol 2 days ago for back pain. On examination, he has hyperreflexia and sustained clonus. Which of the following is the most likely diagnosis?

Answer: C. This patient presents with the classic triad of serotonin syndrome: altered mental status, autonomic instability (hyperthermia, diaphoresis), and neuromuscular excitation (hyperreflexia, clonus). The combination of an SSRI (citalopram) with tramadol (which has serotonergic properties) precipitated this condition. Neuroleptic malignant syndrome presents with rigidity and hyperthermia but is associated with antipsychotics and develops more slowly. Anticholinergic toxicity causes hyperthermia and confusion but with dry skin and absent bowel sounds. Malignant hyperthermia occurs during anesthesia with volatile agents or succinylcholine. Meningitis would show neck stiffness and does not explain the hyperreflexia and clonus.

3. A 35-year-old woman with major depressive disorder has been taking citalopram 40 mg daily for 6 weeks but reports persistent low mood and anhedonia. She denies suicidal ideation. Her only other medication is ibuprofen as needed for headaches. Before this episode, she had one previous depressive episode 5 years ago that responded well to sertraline. Which of the following is the most appropriate next step?

Answer: E. After an adequate trial (4-6 weeks at therapeutic dose) with insufficient response, switching to another antidepressant is appropriate. Sertraline is particularly reasonable given her prior positive response to it. Increasing citalopram above 40 mg daily is contraindicated due to QT prolongation risk. Waiting another 4 weeks delays potentially effective treatment when current response is inadequate. Switching to escitalopram may help but offers no clear advantage when she previously responded to sertraline. Augmentation with aripiprazole is typically reserved for treatment-resistant depression after trials of multiple antidepressants, not as a second-line strategy.

Frequently asked questions

How does citalopram work?

Citalopram works by selectively blocking the serotonin reuptake transporter (SERT) in the brain, preventing serotonin from being reabsorbed into nerve cells after it is released. This increases the amount of serotonin available in the synaptic space between neurons, enhancing serotonergic neurotransmission. The elevated serotonin levels are thought to improve mood and reduce anxiety, though the full therapeutic effect typically requires 2-4 weeks of treatment as the brain adapts to the increased serotonin availability.

What are the side effects of citalopram?

Common side effects include nausea, dry mouth, insomnia or drowsiness, sweating, and sexual dysfunction (affecting 30-40% of patients). The most serious concern is dose-dependent QT interval prolongation on ECG, which can lead to dangerous heart rhythm abnormalities. Other significant risks include serotonin syndrome when combined with other serotonergic drugs, increased bleeding risk (especially with blood thinners), hyponatremia (low sodium), and increased suicidal thoughts in young adults under 25. Abruptly stopping citalopram can cause withdrawal symptoms including dizziness, nausea, and irritability.

What is the maximum dose of citalopram?

The maximum dose of citalopram is 40 mg per day in most adults due to the risk of QT interval prolongation on ECG. However, certain populations require a lower maximum of 20 mg daily: patients over 60 years old, those with liver disease, those taking CYP2C19 inhibitor medications, and CYP2C19 poor metabolizers. These dose restrictions were implemented after studies showed that higher doses cause clinically significant QT prolongation, which can predispose to dangerous cardiac arrhythmias.

Is citalopram a controlled substance?

No, citalopram is not a controlled substance. Unlike benzodiazepines, opioids, and stimulants, SSRIs like citalopram have no abuse potential and do not cause physical dependence or addiction. However, discontinuing citalopram abruptly can cause uncomfortable withdrawal symptoms (discontinuation syndrome), so the medication should be tapered gradually when stopping treatment. This withdrawal phenomenon is not the same as addiction but rather represents the body's adjustment to the absence of the medication.

Citalopram vs escitalopram — what is the difference?

Escitalopram is the purified S-enantiomer of citalopram, meaning it contains only the therapeutically active form of the molecule, while citalopram is a racemic mixture containing both S- and R-enantiomers. Escitalopram is generally preferred because it achieves therapeutic effects at lower doses (10-20 mg vs 20-40 mg) and does not have the same QT prolongation concerns at therapeutic doses that limit citalopram dosing. Both are effective SSRIs with similar side effect profiles, but escitalopram's improved safety profile regarding cardiac effects makes it a more common first choice.

Conditions it is used for

Major depressive disorderGeneralized anxiety disorderPanic disorderSocial anxiety disorderObsessive-compulsive disorderPost-traumatic stress disorder
EscitalopramSertralineFluoxetineParoxetineFluvoxamineVenlafaxineDuloxetineBupropion

Sources and further reading

DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: N06AB04

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.