Do Antibiotics Affect Birth Control Pills?

Birth control pills or oral contraceptives entered the market in the 1960s and since then they have become an integral part of many women’s lives all over the world. And it’s pretty clear why - they are easy-to-use and in almost 100% of cases can prevent unwanted pregnancies. Like other drugs without prescription, such pills can be purchased from a pharmacy or an online store.

Knowing the potential drug interactions of oral contraceptives is critically important both in terms of preventing unwanted pregnancies and in terms of contraception safety. The potential and the type of drug interactions of such pills are determined by the pharmacokinetics of their ingredients. Oral contraceptives can be divided into two main groups – progestin-only pills and those containing the combination of estrogen and progestin.

The metabolism of oral contraceptives can change under the influence of a number of medications that can either increase or decrease the levels of progestin or estrogen in the body. Increased metabolism of birth control pills leads to their reduced activity, and therefore increases the possibility of unwanted pregnancy. Many antimicrobial medications can enhance the metabolism of these pills; however, clinically significant interactions are observed not in all cases.

A number of studies have shown that concomitant use of oral contraceptives and antibiotics leads to contraception failure in 1.2-1.6 % of cases. As a comparison, it should be noted that if birth control pills are used improperly, the ratio of contraception failures is about 5%. It has also been proved that such antibiotic medication as Rifampicin enhances metabolism of oral contraceptives.  There are conflicting reports concerning other antibiotics like Amoxicillin, Penicillin, Metronidazole. According to some researchers, they do not interact with oral contraceptives, whereas other scientists point out that there are clinically significant interactions between these antibiotics and the pills that reduce efficiency of the latter.

So, many doctors claim that more research is required to completely eliminate any possibility that antibiotics affect birth control. To be on the safe side, healthcare providers recommend those women who are undergoing any antibacterial therapy should use additional non-hormonal birth control methods like condoms, cervical cap, diaphragm or contraceptive sponge.