According to a new study, your weight may have an impact on the effectiveness of the morning-after pill. The study, conducted in 2011, is based on the French morning-after pill called Norvelo.
What is important is that the Norvelo pill is identical to the Plan B One-Step, which also has the generic name of Next Choice One Dose, and My Way that are sold in the United States. These types of pills contain a synthetic version of the hormone progestogen called levonorgestrel.
The study revealed that Norlevo began losing its effectiveness when women weighed more than 165 pounds, but it also revealed that for women over 176 it showed an "absence of effectiveness."
Beginning in 2014, the French product will come with a new label warning women that the pill may not be effective for women over a certain weight. However, the FDA and makers of U.S. morning-after pills have not made a decision to change their packaging.
According to Anna Glasier, an expert in reproductive medicine at the University of Edinburgh, it is unclear as to why emergency contraceptives may be less effective for overweight women.
In an interview with CNN, Glasier said, "There has been some evidence over the years that low doses of progestogen-only contraceptives have less efficacy in heavier women, but we do not know why. It is well recognized that body weight affects the way drugs are metabolized."
The study also found that "obese women had three times the risk of getting pregnant after taking emergency contraception than those with a normal body weight."
The exact reason for the ineffectiveness among larger women is unknown. However, other research has shown that women who weighed more than 155 pounds are at a higher risk of regular oral contraception failure.
One study discovered that it takes "longer to reach normal concentration levels in the blood of obese women compared with normal weight women."
If you are concerned about the effectiveness of your morning-after pill discuss possible options with the pharmacist and/or doctor.
Options you might want to consider include using an emergency contraceptive with ulipristal acetate.