I have heard time and time again that antibiotics decrease the effectiveness of Birth Control pills. Birth Control pills taken under perfect conditions are 99% effective and taken under normal circumstances are 92% effective. There is always a chance that even if you take the pill under perfect conditions that you could have an unwanted pregnancy, that being said it is better to be safe and use a second form of protection. But I wanted to find out if Antibiotics actually had an impact.

Studies are very mixed in their findings. One study has found that there are two ways that Antibiotics can potentially reduce the effectiveness of Birth Control pills. One of these ways centers around the fact that Birth Control contain estrogen and certain antibiotics cause enzymes in the liver to break down estrogen which lowers the levels in the body and therefore could effect how well the Birth Control works. Another one of the ways this study found was that antibiotics reduce the re-circulation of estrogens in the body.

Another study found that the only drug that has been proven to make Birth Control less effective is Rafampin. Rafampin lowers the effects of Birth Control by decreasing the hormone levels in the women. It has also been shown to lower the effects of the Birth Control Patch. Some antifungal medicine like griseofulvin has been said to potentially lower levels of Birth Control hormones and in turn reduce the effectiveness of Birth Control pills. There are also some HIV medications that have been said to affect the effectiveness.

Other drugs however, have shown no decline in the effectiveness of Birth Control. In 2002 a study by the Journal of the American Academy of Dermatology found that ampicillin, ciprofloxacin, doxycycline and several other drugs had no effect in lowering the levels of hormones in the body. An observational trial looked at the records of three different dermatology practices and surveyed 356 patients with a history of taking antibiotics and oral contraceptives. This study has 162 patients as “control” data by not taking any antibiotics through the trial, and the remaining 263 provided control data when they were not on antibiotics. The results of this trial were that five pregnancies occurred in the 311 women with both antibiotic and oral contraceptives (1.6%). This statistic is not deemed significant because naturally Birth Control has a 1% chance of failing. All the data covered had failure rates below 3% which is typical for the US. This study suggests that antibiotics do not increase the risk of pregnancy.

So all in all it is always better to play it safe and use a second form of protection, but just because you are on antibiotics does not mean your Birth Control will work any worse. Medical companies put out the warning to cover themselves from potential lawsuits and problems but there is not enough evidence to say that Antibiotics decrease the effectiveness of Birth Control pills, so do what you want at your own risk.