The effectiveness of Opill may be reduced by hepatic enzyme–inducing drugs that treat certain disorders, such as3: Seizures (barbiturates, carbamazepine, oxcarbazepine, phenytoin, topiramate, primidone) Tuberculosis (rifampin, rifabutin) Pulmonary hypertension (bosentan) HIV/AIDS (efavirenz) Additionally, St John’s Wort (or any herbal products containing hypericum perforatum) may interfere with Opill’s efficacy.3 During concomitant use of Opill and substances that may affect its efficacy, individuals should use a nonhormonal backup method of contraception (such as a condom).35 If emergency contraception (morning-after pill) has been taken within the last 5 days3: Opill should not be used for 5 days after using the emergency contraceptive ulipristal acetate, as it may reduce the effectiveness of both Opill and the emergency contraceptive A condom (or other barrier method) should be used during sex until the next period