Brian Staiger asked
My doctor prescribed amoxicillin for strep. I am worried it will affect my birth control pills. Can you answer whether or not my amoxicillin prescription interacts with my birth control?
Answer
It is always worrisome to take begin a medication that may interact with your birth control. It is important to protect against the serious consequence of unplanned pregnancy. Antibiotics (such as amoxicillin) are the medications that are most commonly associated with a loss in efficacy of birth control.
Unfortunately, the answer as to whether or not amoxicillin reduces the efficacy of birth control is not a simple 'yes' or 'no' as there is conflicting data on the subject.
When discussing this subject, it important to note that there is only one class of antibiotics that we are absolutely sure negatively affects birth control and that is the 'rifamycin' class of antibiotics. Rifamycin antibioitics decrease concentrations of both estrogen and progestin hormones in the body, leading to reduced effectiveness of birth control.
How other antibiotics such as amoxicillin affect birth control is less conclusive.
The majority of studies shown that most antibiotics do not significantly reduce the concentrations of oral contraceptives in the body and the efficacy of birth control pills is unchanged.
The problem is this: some studies note that there are a small number of individual patients who do in fact experience a significant decrease in concentrations of oral contraceptives and appear to ovulate (which birth control pills are supposed to suppress). Unfortunately, it is difficult to identify exactly who is susceptible.
In addition, antibiotics are known to cause changes to our normal bacterial gut flora and the metabolism of the hormones in birth control is partially mediated by the bacteria in our gut. This theoretically can affect the effectiveness of birth conrol.
The general consensus appears to be that most antibiotics do not pose a problem in those on birth control BUT women who may be affected are not easily identified and the true number of incidence of pregnancy while on antibiotics may be under-reported in total.
Since unplanned pregnancy has major consequences, it may be prudent to use an additional method of contraception during your amoxicillin therapy, just to be safe.
