One study suggests that
lamotrigine does not alter the contraceptive
efficacy or
plasma levels of combined oral
contraceptives. Another study found a slight reduction in levonorgestrel levels but no evidence of ovulation. Hormonal
contraceptives may reduce the levels of
lamotrigine, which can lead to a decrease in seizure
control.
The manufacturers suggest that reduced contraceptive
efficacy cannot be ruled out, and recommend the use of non-hormonal
contraceptives. However, the FFPRHC has found no evidence of reduced contraceptive
efficacy and so they suggest that there is no good evidence that non-hormonal methods of contracep- tion are preferable.
Lamotrigine can be started as normal in patients already taking hormonal
contraceptives. For women already taking
lamotrigine and carbamaze- pine or
phenytoin no
lamotrigine dosage adjustment is necessary when hormonal
contraceptives are started, but in the absence of these other antiepileptics the maintenance dose of
lamotrigine may need to be increased by as much as twofold, according to
clinical response. Patients should also be advised that an increase in seizure frequency may occur when the combined oral contraceptive is started.