For the Overweight and Obese, Oral and Emergency Contraceptives Can Lack Efficacy

The European “morning-after pill” Norlevo®, which is identical in formula to the U.S. drug Plan B One-Step®, announced that it will be updating its packaging to warn consumers that it is not effective in women who weigh more than 176 pounds. In fact, obese women who used emergency contraception were three times more likely for the pill to fail than women of normal weight, according to a 2011 study. With approximately one-third of U.S. adults being obese, this news may be troubling to individuals who have relied on Plan B One-Step in the past as a backup method of birth control.

Plan B One-Step is a non-prescription, over-the-counter emergency contraceptive that is available to women of all ages. It reduces the chance of a woman getting pregnant after unprotected sex or birth control failure by stopping the release of an egg from the ovary.

Norvelo contains 1.5 mg of levonorgesterol, the same amount as Plan B One-Step. HRA Pharma, the manufacturer of the drug, has stated that increasing the dosage of the ingredient does not increase protection for women who weigh more than 165 pounds. The manufacturer of Plan B One-Step, Teva Pharmaceutical Industries, has not commented on whether it will release a similar warning.

Emergency contraception pills are not the only form of birth control whose effectiveness can be affected by weight. Oral contraceptives (the pill) have also been found by researchers to have a higher chance of failure in obese women. While the effective blood concentrations can eventually be reached when taking the pill, the “window of opportunity” for pregnancy can be twice as long in obese women, about 10 days instead of the typical 5 days.

Overweight and obese women who take the pill or occasionally rely on emergency contraception should use a backup form of protection such as condoms (at least for the first 10 days of the pack for users of the pill), or talk to their doctors about other options such as intrauterine devices (IUDs).