Birth Control Pills and Antibiotic Use

By Freedman, Megan

Do you know that you can get pregnant while taking antibiotics, even if you’re taking birth control pills? Not all antibiotics have this effect. But to be safe, before starting an antibiotic, tell your healthcare provider that you are on the pill and ask if you should use a backup form of birth control temporarily.

How Do Antibiotics Affect Birth Control Pills?

The birth control pill, commonly called “the pill," is a medication women take once a day to prevent pregnancy. One way birth control pills prevent pregnancy is by preventing ovulation—when your body releases an egg that can be fertilized by a male sperm. Some antibiotics can interfere with your menstrual cycle, causing you to ovulate even though you’re on the pill.

Which Antibiotics Are More Likely to Interfere With the Pill?

Not all antibiotics will increase your chances of getting pregnant on the pill. However, one particular antibiotic, called rifampin (Rifadin, Rimactane), can interfere with your menstrual cycle and reduce the effectiveness of birth control pills. While rifampin is less commonly prescribed today, other types of antibiotics may also have the same effect.

You may wonder how an antibiotic could possibly affect your birth control pill. In the case of rifampin, scientific studies have shown that it decreases blood levels of both ethinyl estradiol and the progestins contained in birth control pills. If their blood levels fall too low, the hormones can’t do their job of preventing ovulation. The mechanism is complex, but basically rifampin stimulates your liver to process and get rid of these hormones faster than normal.

The data are not so clear for other antibiotics, so the interaction remains controversial. Unlike rifampin, there aren’t conclusive scientific studies for other antibiotics. But there are various theories about how other antibiotics might interfere with your birth control pill. Some of these theories are even more complex than rifampin’s interaction. Basically, the theories suggest that antibiotics may decrease the amount of hormones your body absorbs. However, none of them are solidly proven.

Talk with your healthcare provider or pharmacist before starting an antibiotic. Ask if it will change the effectiveness of your birth control pills or other hormone-based birth control you may be taking, such as an implant, shot or patch. If you have any worries or doubts about taking an antibiotic with your birth control pill, be safe and use a backup method of birth control. It can’t hurt and it may put your mind at ease.

How Can I Prevent Pregnancy If I'm Taking Antibiotics?

It is not likely that you will get pregnant while taking antibiotics on the pill. But it doesn't hurt to be extra cautious. To be safe, use a backup method of birth control while you take your antibiotics and for up to a week after you finish. Backup birth control options you can try include condoms, sponges and spermicide. You can buy these forms of birth control without a prescription at many grocery stores and drugstores.

Do not stop taking your birth control pills even if you are temporarily using a backup method of birth control. Take your pills exactly as you always have to avoid messing up your cycle.

Medical Reviewer: William C. Lloyd III, MD, FACS Last Annual Review Date: Dec. 15, 2013 Copyright: © Copyright 2013 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

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