The birth control pill is used by many women for prevention of pregnancy. While generally very effective to prevent pregnancy if taken correctly, failure to prevent pregnancy can occur.
It has been noted in observational studies that women with obesity may have a higher risk of birth control pill failure, compared to women without obesity. How could this be?
It turns out that the oral contraceptive has altered pharmacokinetics in obesity – meaning that the way the body handles the medication is a little bit different. Specifically, some research has suggested that the half life of the birth control pill is longer, meaning that it takes longer for the pill to reach therapeutic levels in women with obesity (ie at the beginning of the pack each month).
Strategies to minimize birth control pill failure in women with obesity have been suggested, such as taking the pill continuously, or using a higher dose than the low dose regimens that are commonly prescribed. However, these strategies would have to be weighed against the potential for increased risks such as potential increased risk of blood clots with higher estrogen exposure. One thing I feel we can conclude from this information is that taking the pill correctly (not starting a new pack late, not missing doses, and taking it within the required time frame each day) is especially important.