The Relationship Between Oral Birth Control and Antibiotics
Myth: All antibiotics reduce the effectiveness of birth control pills.
Fact: Most prescription antibiotics and oral contraceptives come with safety inserts that warn of certain drugs that can compromise the effectiveness of oral contraceptives. Research has revealed that one drug, Rifampin, may interfere with birth control.
Medications that Reduce Oral Contraceptive Effectiveness
Rifampin (other possible brand names include Rifampicin, Rifamycin, Rimactane, Rifadin, Rifamate) is a medication used to treat tuberculosis-a potentially serious infectious disease that usually affects the lungs but may also affect other parts of the body. It is also used to eliminate bacteria from the nose and mouth in order to prevent the spread of meningitis bacteria. Talk to your doctor if you are using hormonal contraception (birth control pills, patches, rings, implants, injections). Rifampin will reduce the effectiveness of hormonal contraception, so it is recommended you use another form of birth control while taking it.1 Rifampin affects certain liver enzymes, which speeds up the removal of other drugs (such as estrogen and progestin found in oral contraception) from the body.2 The effects of this chemical interaction may last for several weeks after the user stops taking Rifampin.3 Aside from Rifampin, there has been no link found between oral contraceptive failure and the use of antibiotics.
However, certain medicines and supplements may also reduce the effectiveness of oral contraception. These include the following:
- The antifungal Griseofulvin
- Certain HIV medications
- Certain anti-seizure medications
- St. John’s wort
The Effect of Most Antibiotics on Birth Control
A 2011 Harvard study4 looked at oral birth control failure rates between females who took antibiotics in the four weeks before conception and those who did not. The study included more than 43,000 females taking antibiotics and oral contraception simultaneously. The most common antibiotics taken were amoxicillin/ampicillin followed by macrolides and sulfonamides. In this study, 1,330 of the 43,000 women became pregnant while taking oral contraception and antibiotics simultaneously, which contributed to a failure rate of approximately 3%.4 This failure rate falls within the 1-9% typical use failure rate of oral contraception. This typical use failure rate means that out of every 100 women who use oral contraceptives, 1 to 9 women will become pregnant within the first year of use due to human errors (such as forgetting a pill or taking a pill late). The perfect use failure rate of oral contraception, when it is taken correctly and consistently every time, is much lower (<1%).5 Since individuals using both oral contraception and antibiotics are subject to typical use failure rates, the results of the study follow predicted values and show that antibiotics (aside from Rifampin) do not reduce the effectiveness of oral contraception. The study also found that neither acetaminophen nor ibuprofen was associated with a greater risk of oral contraceptive failure.4
Two earlier studies, published in 1997 and 2002 respectively, also found no difference in the failure rates of oral contraception between females who were taking antibiotics and those who were not.
What You Can Do
Despite the lack of evidence produced so far, doctors say that more research may be necessary to completely rule out the possibility that antibiotics do not affect birth control. Studies on this topic have not been sizeable enough to produce conclusive results, simply because not many females get pregnant while taking birth control pills and antibiotics at the same time. Concerned patients should talk with their doctors and take all medications exactly as directed. Using a non-hormonal back up form of contraception (like a male or female condom, diaphragm, or copper IUD) can further reduce the risk of pregnancy.
1. "Rifampin: MedlinePlus Drug Information." U.S National Library of Medicine. American Society of Health-System Pharmacists, 15 Dec. 2012. Web. 11 Feb. 2015. <http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682403.html>."RIFAMPIN - ORAL (Rifadin, Rimactane) Side Effects, Medical Uses, and Drug Interactions." MedicineNet. N.p., 16 Apr. 2014. Web. 11 Feb. 2015. <http://www.medicinenet.com/rifampin-oral/page3.htm>.
2. "Interactions between Rifampin Oral and Rifamycins-estrogens-contraceptives." WebMD. WebMD, n.d. Web. 11 Feb. 2015. <http://www.webmd.com/drugs/2/drug-1744/rifampin-oral/details/list-intera....
3. Toh, S., AA Mitchell, M. Anderka, LT De Jong-van Den, and S. Hernandez-Dias. "Antibiotics and Oral Contraceptive Failure- a Case-crossover Study." US National Library of Medicine. PubMed, 8 Oct. 2010. Web. 11 Feb. 2015. <http://www.ncbi.nlm.nih.gov/pubmed/21477683>.
4. "Contraceptive Technology Failure Table." Contraceptive Technology. N.p., Sept. 2013. Web. 11 Feb. 2015. <http://www.contraceptivetechnology.org/wp-content/uploads/2013/09/CTFail....
5. Helms, SE, DL Bredle, J. Zajic, D. Jarjoura, RT Brodell, and I. Krishnarao. "Result Filters." US National Library of Medicine. PubMed, 1 May 1997. Web. 11 Feb. 2015. <http://www.ncbi.nlm.nih.gov/pubmed/9146531>.
6. Archer, JS, and DF Archer. "Result Filters." US National Library of Medicine. PubMed, 1 June 2002. Web. 11 Feb. 2015. <http://www.ncbi.nlm.nih.gov/pubmed/12063491>.
Last Updated 26 February 2015.