skip to main content

Lamotrigine-COC interaction — GPhC CRA MCQ

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

ModerateCNS TherapeuticsLamotrigine-COC interactionGPhC CRA

A 25-year-old woman taking lamotrigine 200 mg daily for bipolar disorder tells the pharmacist she has just started the combined oral contraceptive pill (ethinylestradiol/levonorgestrel). What is the most important concern?

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

Reveal the answer and explanation

Correct answer: B — Ethinylestradiol increases lamotrigine clearance, potentially reducing seizure or mood control

Ethinylestradiol-containing contraceptives induce the glucuronidation of lamotrigine, significantly reducing its plasma levels (by up to 50%). This can lead to loss of seizure or mood control. Conversely, during the pill-free week, lamotrigine levels can rise rapidly, potentially causing toxicity. The prescriber should be contacted to review the lamotrigine dose or consider an alternative contraceptive method (such as a progestogen-only method, which does not affect lamotrigine levels).

Reference: BNF Drug Interactions; FSRH; MHRA