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Opioid-Benzodiazepine Risk — MRCPsych Paper B MCQ

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ModerateSubstance MisuseOpioid-Benzodiazepine RiskMRCPsych Paper B

A 35-year-old man has been stable on methadone maintenance treatment at 70 mg daily for 6 months. He reports taking illicit benzodiazepine tablets several evenings each week. He says that he usually remains alert and believes his stable methadone dose makes the combination safe. Which statement best explains the principal danger of this combination?

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

Reveal the answer and explanation

Correct answer: D — Additive CNS depression increases the risk of respiratory depression and death

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

Methadone and benzodiazepines both depress the central nervous system. Their effects are additive, increasing sedation and potentially causing respiratory depression, coma and death. Remaining alert on previous occasions does not establish safety, particularly because illicit tablets may have uncertain content and methadone-related respiratory depression can be delayed. Benzodiazepines do not characteristically induce methadone metabolism or antagonise opioid receptors, so A and C are incorrect. There is no relevant interaction based on reduced benzodiazepine absorption, excluding D. Methadone can prolong the QT interval, especially at higher doses or with additional risk factors, but benzodiazepines are not principally dangerous in this combination through synergistic QT prolongation, making E less appropriate.

Reference: Methadone Mixture 1 mg/ml, Summary of Product Characteristics, sections 4.4 and 4.5 (current version, eMC). https://www.medicines.org.uk/emc/product/4907/smpc