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Atomoxetine mechanism — MRCPsych Paper A MCQ

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HardPsychopharmacologyAtomoxetine mechanismMRCPsych Paper A

A 13-year-old girl has ADHD and a chronic tic disorder. Her tics were not worsened by stimulants, but her ADHD symptoms remain impairing after separate adequate trials of methylphenidate and lisdexamfetamine. Atomoxetine is started. Which option most precisely describes the primary pharmacodynamic action of atomoxetine?

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Correct answer: B — Inhibition of presynaptic noradrenaline transporters without direct dopamine-transporter blockade

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

A is correct. Atomoxetine selectively and potently inhibits the presynaptic noradrenaline transporter, increasing extracellular noradrenaline; it does not directly inhibit dopamine or serotonin transporters. Tic disorder alone does not require avoidance of stimulants, so the revised stem uses NICE-compatible treatment sequencing. Option B describes guanfacine, an alpha-2A-adrenoceptor agonist. Option C describes the principal transporter effects of methylphenidate. Option D describes VMAT2 inhibitors such as tetrabenazine, which deplete monoamine stores and may be used for selected hyperkinetic movement disorders rather than ADHD. Option E describes aripiprazole, which may be used for severe tics in specialist practice but is not an ADHD treatment.

Reference: electronic Medicines Compendium, Atomoxetine 100 mg hard capsules: Summary of Product Characteristics, section 5.1 Pharmacodynamic properties, updated 31 January 2025. https://www.medicines.org.uk/emc/product/100477/smpc