Birth control pills prevent pregnancy very well. Used correctly, they’re more than 99% effective. But, certain things can interfere with effectiveness. For example, many women forget to take their pills regularly. Certain medicines, including over-the-counter drugs and herbals, may also cause the pill to work less well.
Some doctors always warn women who are taking both hormonal birth control and antibiotics to use a back-up method. But, other doctors don’t mention it. What’s the truth? If you’re on the pill and you need to take penicillin for a sore throat, do you need to worry about getting pregnant?
What the Research Shows
For most women, most birth control pills, and most antibiotics, there shouldn’t be a problem. The pill should continue to work well during the week or two you’re taking the medicine. However, medical studies have found that in some women, common antibiotics can reduce the amount of estradiol, or the hormone in birth control pills, in the bloodstream. If the level of estradiol gets too low, the drug won’t work to prevent pregnancy.
How do you know if you’re one of the women who will be affected? Unfortunately, there’s no way to tell. For this reason, it’s a good idea to use a second method of birth control while you’re taking antibiotics.
One specific antibiotic, called rifampin, is especially likely to reduce the pill’s effectiveness. This drug is often prescribed for tuberculosis, and it’s also used against a type of bacteria that causes meningitis. Your doctor may prescribe it for other infections as well. Women taking rifampin should always use a backup method.
Using a Backup Method
Your doctor can help you decide whether you need to use a backup method when you’re taking hormonal birth control and antibiotics. A common recommendation is to use the backup method, along with your birth control pills, for about two weeks. However, what you actually need to do will depend on what antibiotic you’re taking and how long you’re taking it.
Your doctor will probably suggest that you keep taking your pills but also use condoms, a diaphragm, or another barrier method. Other hormonal methods, like the patch or the ring, can also be affected by antibiotics, so you shouldn’t use one of those as your backup.
Other Forms of Birth Control and Antibiotics
The patch and the ring contain hormones similar to the ones in the pill. The manufacturers of these birth control methods warn that antibiotics could prevent them from working properly. Just like with the pill, you should check with your doctor to see if you need to use a backup method.
Barrier methods, including condoms and diaphragms, shouldn’t be affected by antibiotics that you take by mouth. However, if you’re using a cream to treat a yeast infection or other medicine that must be inserted into the vagina, be sure to read the instructions carefully. Some of these medicines can damage condoms and diaphragms, making them ineffective.
Other Drugs that Interfere with Birth Control
According to Planned Parenthood, the following drugs can reduce the effectiveness of the birth control pill, ring, and patch:
- Certain anti-fungal medicines, taken by mouth for yeast infections
- Certain anti-HIV protease inhibitors
- Some anti-seizure medications
- St. John’s Wort
Always check with your doctor if you have a question about any medicine. Your doctor will know about recent research and can give you information about specific types of birth control and antibiotics. If it’s extremely important that you not get pregnant, be sure to let your doctor know. Even if the antibiotic hasn’t been proven to interfere with birth control, your doctor may recommend a backup method anyway, just in case.