The recent studies indicate that various antibiotics might reduce the effectiveness of birth control pills, usually affecting the metabolism needed for the birth control pill. However, the changes were not found for more than one percent, which might be taken as insignificant compared to the birth control pill effectiveness rate which ranges from 95 to 99 percent in different studies. Using a barrier form of birth control is highly recommended to increase the chances for preventing unwanted pregnancy.


The exact number of days needed for the hormones from the birth control pills to reach the wanted levels in the blood, after taking antibiotics might not be more than the time they need to reach the same level when starting to take the birth control pills in the first place. As it is recommended to use other forms of birth control in the first seven days of taking the birth control pills, seven days might be enough for the hormones to reach the wanted levels.


You might want to consult with your gynecologist for additional information about the metabolic degradation interference between the antibiotic you took and the particular birth control pill you are using.