What Medication Can Affect Oral Contraceptives?

Women depend on oral contraceptives to work consistently, without exception. But some other commonly prescribed medications can alter the effectiveness of birth control pills. How can you be sure that your other prescription medicine is safe to take with your birth control pills? There are four types of medication that might interfere with oral contraceptives.

Antibiotics

• Certain antibiotics can disrupt the action of oral contraceptives. According to a Nov. 1, 1999, article in the magazine American Family Physician, "Rifampin (Rifadin) is the only antibiotic that has been shown to ... significantly reduce the efficacy of oral contraceptive pills." However, the study also indicates that ampicillin, amoxicillin, metronidazole (Flagyl) and tetracycline may be associated with oral contraceptive failure.

Migraine medication

• Topamax, a drug prescribed for migraines as well as seizures, "may also make the oral contraceptive pill less effective at Topamax doses of 200 mg or more," according to the Epilepsy Foundation of America.

Anti-seizure medication

• Some antiepileptic drugs can significantly increase the risk for an unplanned pregnancy, including carbamazepine (Tegretol), phenytoin (Dilantin), phenobarbital, primidone (Mysoline), ethosuximide (Zarontin) and troglitazone (Rezulin), according to American Family Physician. As reported above, Topamax may also interfere with birth control pills.

St. John's Wort

• A December 2003 study published in the British Journal of Pharmacology showed that in women taking both low-dose contraceptive pills and St. John's Wort, mid-cycle "bleeding episodes increased," causing difficulty in following the oral contraceptive routine, which might "enhance the risk of unintended pregnancies."

Warning

• Always consult your doctor and your pharmacist with questions about medications you have been prescribed.

  Never take a medication that was prescribed for someone else.

  Never stop taking medication that was prescribed for you without consulting your doctor or pharmacist.