Drug maker GlaxoSmithKline has issued a “Dear Doctor” letter advising that its anti-epilepsy drug Lamictal (lamotrigine) can reduce the effectiveness of oral contraceptives.

New data have demonstrated an interaction between combined oral contraceptives and lamotrigine which could lead to reduced effectiveness of hormonal contraceptives, a revised product label states.

“Women should have a review of their contraception when starting lamotrigine, and the use of alternative non-hormonal methods of contraception should be encouraged,” the new label states.

It adds: “A hormonal contraceptive should only be used as the sole method of contraception if there is no other alternative.”

“If the oral contraceptive pill is chosen as the sole method of contraception, women should be advised to promptly notify their physician if they experience changes in menstrual pattern (e.g. breakthrough bleeding) while taking Lamictal as this may be an indication of decreased contraceptive efficacy.”

Lamotrigine concentrations are cut in half during co-administration of oral contraceptives, the label further states.

“This may result in reduced seizure control in women on a stable lamotrigine dose who start an oral contraceptive, or in adverse effects following withdrawal of an oral contraceptive. Dose adjustments of lamotrigine may be required,” it advised.