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:
St. John's wort may cause your body to process your estrogen or your contraceptives more quickly.
What might happen:
St. John's wort may reduce the effectiveness of your estrogen, which may result in symptoms of menopause or your contraceptive, which may lead to pregnancy.
What you should do about this interaction:
Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking St. John's wort. Report any changes in your menstrual cycle, such as spotting or breakthrough bleeding, to your healthcare professional. Your doctor may want to change your oral contraceptive dose or may suggest you consider using another form of birth control while taking St. John's wort. You may need to stop taking St. John's wort. Let your healthcare providers know if you stop taking St. John's wort while you are taking your estrogen or contraceptive.Your healthcare professionals may already 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.Premarin (conjugated estrogens) US prescribing information. Wyeth Pharmaceuticals July, 2006.
2.Anonymous. From the Food and Drug Administration. JAMA 2000 Apr 5; 283(13):1679.
3.Hall SD, Wang Z, Huang SM, Hamman MA, Vasavada N, Adigun AQ, Hilligoss JK, Miller M, Gorski JC. The interaction between St John's wort and an oral contraceptive. Clin Pharmacol Ther 2003 Dec;74(6):525-35.
4.Pfrunder A, Schiesser M, Gerber S, Haschke M, Bitzer J, Drewe J. Interaction of St John's wort with low-dose oral contraceptive therapy: a randomized controlled trial. Br J Clin Pharmacol 2003 Dec;56(6):683-90.
5.Nor-Q-D (norethindrone) US prescribing information. WatsonPharma March, 2005.
6.Murphy PA, Kern SE, Stanczyk FZ, Westhoff CL. Interaction of St. John's Wort with oral contraceptives: effects on the pharmacokinetics of norethindrone and ethinyl estradiol, ovarian activity and breakthrough bleeding. Contraception 2005 Jun;71(6):402-8.
7.Schwarz UI, Buschel B, Kirch W. Unwanted pregnancy on self-medication with St John's wort despite hormonal contraception. Br J Clin Pharmacol 2003 Jan;55(1):112-3.
8.Fogle RH, Murphy PA, Westhoff CL, Stanczyk FZ. Does St. John's wort interfere with the antiandrogenic effect of oral contraceptive pills?. Contraception 2006 Sep;74(3):245-8.