Mechanism of action of SSRIs — MRCPsych Paper A MCQ

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EasyPsychopharmacologyMechanism of action of SSRIsMRCPsych Paper A

A 29-year-old woman with recurrent depressive episodes starts sertraline after psychological therapy has not helped. Two weeks later she reports mild nausea but no neurological signs. What is the most likely mechanism of action?

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Correct answer: D — Inhibition of serotonin reuptake at SERT

Sertraline is a selective serotonin reuptake inhibitor (SSRI). It inhibits the serotonin transporter (SERT), reducing neuronal serotonin reuptake and thereby increasing serotonergic neurotransmission. Mild nausea is a common early adverse effect and is often transient. NMDA receptor antagonism is associated with drugs such as ketamine; positive GABA-A modulation describes benzodiazepines and related sedatives; monoamine oxidase A inhibition is the mechanism of drugs such as moclobemide; and dopamine D2 receptor blockade is characteristic of many antipsychotics. The absence of neurological or autonomic abnormalities also provides no evidence of serotonin syndrome.

Reference: Electronic Medicines Compendium (emc), Sertraline 50 mg Film-Coated Tablets, Summary of Product Characteristics, sections 5.1 and 4.8, updated 26 March 2026. https://www.medicines.org.uk/emc/product/102002/smpc