Oestrogen-containing contraceptives induce the glucuronidation that clears lamotrigine, lowering its levels substantially. During the pill-free week levels rise again, and some patients notice side effects such as dizziness or double vision.
The interaction runs in the opposite direction to the enzyme-inducer problem: here the contraceptive affects the antiseizure drug. Starting combined contraception can lead to breakthrough seizures, and stopping it can cause lamotrigine toxicity. Progestogen-only methods do not have this effect to the same degree.
- Ask about oestrogen-containing contraception in anyone taking lamotrigine.
- Expect lamotrigine levels to fall when combined contraception starts; a dose increase may be needed.
- Watch for toxicity when combined contraception stops; a dose reduction may be needed.
- Consider continuous rather than cyclical regimens to avoid pill-free fluctuation.
- Pregnancy lowers lamotrigine levels in a similar way.
Why it matters
Breakthrough seizures after starting the pill are often blamed on adherence rather than this interaction.
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