Primidone is an anti-seizure medicine, and it can make Levonorgestrel [For emergency contraception] work less well. If you take the two together, the emergency contraceptive may not protect you from pregnancy as it should. Other medicines that act in the same way include phenobarbitone, phenytoin, carbamazepine, rifampicin and griseofulvin. If you take primidone, talk to a doctor or pharmacist before relying on Levonorgestrel [For emergency contraception].
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.