Norix 1 Levonorgestrel [For emergency contraception] Rifampicin
ModerateRifampicin can make Levonorgestrel [for emergency contraception] work less well, or stop it working at all. The same is true of some epilepsy medicines (phenobarbitone, phenytoin, primidone, carbamazepine) and of griseofulvin. If you are taking rifampicin, the emergency pill may not protect you from pregnancy as it should.
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.