Ketamine neurochemistry — MRCPsych Paper A MCQ

Instant feedback + full explanation. One question, done properly.

EasyNeurophysiology and neurochemistryKetamine neurochemistryMRCPsych Paper A

A 38-year-old woman develops transient depersonalisation and perceptual distortion shortly after receiving ketamine in a monitored treatment setting. Which pharmacological action most directly accounts for these acute dissociative effects?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Antagonism of NMDA-type glutamate receptors

Ketamine is principally an uncompetitive antagonist at NMDA-type glutamate receptors. Disruption of NMDA-mediated signalling in cortical and thalamocortical networks produces its characteristic acute dissociative effects, including depersonalisation, altered awareness and perceptual distortion. Muscarinic receptor agonism would produce cholinergic effects rather than ketamine's dissociative syndrome. Dopamine D2 receptor antagonism is characteristic of antipsychotic action, while 5-HT3 receptor antagonism is principally associated with antiemetic effects. GABA-B receptor agonism, as produced by baclofen, causes inhibitory effects such as sedation and muscle relaxation but is not ketamine's principal mechanism. Therefore, NMDA-type glutamate receptor antagonism is the single best answer.

Reference: hameln pharma ltd. Ketamine 50 mg/ml Injection, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties. Revised 31 July 2025; updated on eMC 5 August 2025. https://www.medicines.org.uk/emc/product/6935/smpc