Unexpected bleeding or reduced contraceptive effect w/ antiepileptics (eg, primidone, phenytoin, barbiturates, carbamazepine, oxcarbazepine), anti-TB drugs (eg, rifampicin), HIV drugs (eg, ritonavir, nevirapine), antibiotics (eg, griseofulvin, penicillins, tetracyclines), St. John's wort & bosentan. Medicines containing ciclosporin. Increased seizure frequency w/ lamotrigine.