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SSRI Bleeding Risk — MRCPsych Paper B MCQ

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ModerateMood DisordersSSRI Bleeding RiskMRCPsych Paper B

A 72-year-old man with recurrent depressive disorder and non-valvular atrial fibrillation is taking apixaban. Sertraline is being considered. A similar safety concern applies when SSRIs are co-prescribed with aspirin. Which mechanism best explains the clinically relevant interaction?

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Correct answer: A — Reduced platelet serotonin uptake, with impaired platelet aggregation

Explanation lettering: B = shown as A · D = shown as B · E = shown as D · A = shown as E

B is correct. Platelets obtain serotonin through the serotonin transporter. SSRIs inhibit this uptake, reducing intraplatelet serotonin and impairing platelet recruitment and aggregation. This antiplatelet effect can add to the haemostatic effects of aspirin or anticoagulants, increasing bleeding risk, particularly gastrointestinal bleeding. A describes the opposite effect. C is incorrect because the principal class interaction is not accelerated anticoagulant clearance. D would promote thrombosis rather than bleeding. E describes aspirin's irreversible COX-1 inhibition and is not an effect confined to paroxetine; increased bleeding is an SSRI class concern. Co-prescription is not invariably contraindicated, but the indication, individual bleeding risk, warning symptoms and need for gastroprotection should be assessed.

Reference: Electronic Medicines Compendium. Apixaban 2.5 mg film-coated tablets, Summary of Product Characteristics, sections 4.4 and 4.5; updated 10 July 2026. https://www.medicines.org.uk/emc/product/101543/smpc