Effects of hormonal contraception on lamotrigine

Combined hormonal contraceptives increase the metabolism of lamotrigine. This can result in significantly lower serum lamotrigine concentrations (reduced effect) while taking active (hormone) pills, and may result in increased concentrations (risk of toxicity) during the hormone-free interval. If a combined hormonal contraceptive is the most suitable option for a patient, continuous use (use without a hormone-free interval) of a combined oral contraceptive pill or vaginal ring avoids cyclical changes in lamotrigine concentrations. Measure serum lamotrigine concentrations after starting these contraceptives because lamotrigine dosage may need to be increased (possibly up to 2-fold) to maintain efficacy.

Extrapolating from evidence on the desogestrel progestogen-only pill (unavailable in Australia), use of any form of progestogen-only contraception may increase the risk of lamotrigine toxicity. Advise patients taking lamotrigine who start progestogen-only contraception to alert their clinician to any symptoms of toxicity such as dizziness, co-ordination difficulties or double vision.

When starting or stopping hormonal contraception for a patient taking lamotrigine, consult the patient's neurologist or psychiatrist so that any dose adjustments required can be made.