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Lithium Augmentation Level — MRCPsych Paper B MCQ

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HardMood DisordersLithium Augmentation LevelMRCPsych Paper B

A 40-year-old woman with unipolar treatment-resistant depression is commenced on lithium augmentation of her antidepressant. Her renal and thyroid function are normal, and lithium concentrations are measured 12 hours after the last dose. According to current NICE guidance, which statement best describes the plasma lithium concentration target?

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Correct answer: D — Usually at least 0.4 mmol/L, with an upper limit of 1.0 mmol/L

NICE recommends determining the lithium dose according to response and tolerability. For augmentation of antidepressant treatment, the 12-hour plasma lithium concentration is usually at least 0.4 mmol/L and should not exceed 1.0 mmol/L. Thus, B is the best statement rather than a mandatory fixed range. Concentrations below 0.4 mmol/L are generally inadequate for augmentation. The narrower 0.4–0.6 mmol/L range should be considered in people aged 65 years or older, not routinely in this 40-year-old patient. A target extending to 1.2 mmol/L is unnecessarily high for antidepressant augmentation and increases toxicity risk. Lithium targets should be individualised according to indication, response, tolerability and patient factors rather than automatically copied from bipolar-disorder treatment.

Reference: National Institute for Health and Care Excellence. Depression in adults: treatment and management (NG222), recommendation 1.4.28: Use of lithium as augmentation. 2022; last reviewed 30 January 2026. https://www.nice.org.uk/guidance/ng222/chapter/recommendations