Serious. These medicines may interact and cause very harmful effects. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
Efavirenz and nevirapine may speed up how quickly your liver processes your hormonal contraceptive agent.
What might happen:
The blood levels of your contraceptive agent may decrease, causing breakthrough bleeding, spotting, or pregnancy.
What you should do about this interaction:
Contact your healthcare professionals (e.g. doctor or pharmacist) as soon as possible about taking these two medicines together. You should use another form of birth control in addition to your hormonal contraceptive agent while you are taking efavirenz or nevirapine. Because efavirenz stays in your body a long time, you should continue to use another form of birth control with your hormonal contraceptive for 12 weeks after you stop taking efavirenz.Your healthcare professionals may be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Sustiva (efavirenz) US prescribing information. Bristol-Myers Squibb Company March, 2016.
2.Viramune (nevirapine) US prescribing information. Boehringer Ingelheim Pharmaceuticals, Inc. January, 2014.
3.Mildvan D, Yarrish R, Marshak A, Hutman HW, McDonough M, Lamson M, Robinson P. Pharmacokinetic interaction between nevirapine and ethinyl estradiol/norethindrone when administered concurrently to HIV-infected women. J Acquir Immune Defic Syndr 2002 Apr 15;29(5):471-7.