Having a gallbladder removed will not affect the function of birth control pills. After the gallbladder is removed, some people experience loose stools, gas and bloating for a while. In the years that follow, absorption of medicine is no different with or without a gallbladder.

On the other hand, if you get treated with antibiotics around the time that your gallbladder is removed, it is possible that the effectiveness of your birth control pill might be affected for a short time. Certain antibiotics can affect the amount of estrogen in your bloodstream.

The effect on estrogen happens because normal bacteria in your intestine can be killed by antibiotics. Enzymes from your bacteria help to keep estrogen in your gut in its most active form. Some of the antibiotics that have been linked with a lessening of birth control pill effectiveness are ampicillin, penicillin, tetracycline, metronidazole (Flagyl), trimethoprim-sulfamethoxazole (Bactrim, Septra), and a variety of medicines in the cephalosporin group.

After antibiotics, some women on birth control pills experience breakthrough bleeding due to the drop in estrogen. The risk for pregnancy after antibiotics is only slightly higher than the baseline "failure" rate for birth control pills, 1% to 3%. Although the risk is low, some women add an additional protection (such as condoms) during the menstrual cycle month that follows antibiotic use. This is particularly advised if you have experienced breakthrough bleeding following antibiotic use in the past.