How long do antibiotics affect birth control?

The link between antibiotic use and contraceptive failure is controversial. Only one antibiotic, called rifampin (brand names: Rifadin, Rimactane) has been proven in studies to lessen birth control effectiveness.

Rifampin is a special medication used to treat tuberculosis and is not commonly prescribed. Rifampin may reduce the blood levels and effects of the hormones found in birth control.

For women who take rifampin, a nonhormonal method of birth control, for example, the diaphragm, copper IUD or condom, is recommended.

Rifampin can also lower the effectiveness the transdermal birth control patch (Ortho Evra) and the vaginal ring (NuvaRing), so a different form of birth control should be used with these products, too.

Other common antibiotics have not been shown in studies to make the pill less effective.