Oral contraceptives may be less effective in very heavy women, putting them at risk for unplanned pregnancies. Researchers measured blood concentrations of hormones from a birth control pill in 20 women ages 18 to 35. They found that the pill took twice as long to achieve maximum concentration in an obese group as it did in normal-weight women. According to the researchers, the lag leaves a window of opportunity each month for very heavy women to become pregnant. The authors caution that women shouldn’t stop taking the pill without consulting a doctor.
Source: Contraception, August 2009