Emergency contraception is tremendously important for women seeking to prevent pregnancy after unprotected sex. Activists and public health advocates have worked for years to make EC pills more readily available, and have been successful in getting pills such as Plan B available without a prescription or age restrictions.
Emergency contraception pills containing levonorgestrel (including Plan B) may not be right for every woman and situation, however. Though the pills can be taken up to five days after unprotected intercourse, the pills are most effective (95 percent) when taken within 24 hours and become steadily less effective as more time passes. A different type of EC pill — Ella, containing ulipristal — is thought to keep a pretty high level of effectiveness for the full five days.
News this week has raised another issue of emergency contraception effectiveness: EC pills with levonorgestrel seem to be less effective in women weighing more than 165 pounds, and lose their ability to work in women who weigh more 175 than pounds.
This loss of effect happens regardless of whether women are considered overweight or obese according to BMI charts, or are simply tall — despite headlines that almost exclusively focus on “obese women.”
As Linda Prine of the Reproductive Health Access Project said in an interview with NPR: “This is barely overweight. We’re talking about a BMI over 25. So this is probably more than half of American women. This medication would not work for them.”
The Food and Drug administration is reviewing whether makers of levonorgestrel-containing pills (Plan B, Plan B One-Step, Next Choice, My Way) should be required to revise their labels to include a weight warning. In Europe, the label for one identical product (Norlevo) has already been changed to warn about the loss of effectiveness.
For that study, researchers reviewed results from two prior randomized controlled trials to look for factors that could explain rates of emergency contraception failure. Not only did they find that overweight and obese women had much higher risks of pregnancy than “normal” weight women (anywhere from double the risk to more than four times greater), but women with a “normal weight” BMI women who are tall also have greater risks of pregnancy.
The authors note that additional research is needed to determine whether these women could be given higher doses of the drug for improved efficacy.
The researchers also found that while Ella (ulipristal) worked at higher weights than levonorgestrel-containing pills, it, too, lost some effectiveness with increasing weight. At about 194 pounds, ulipristal appeared to lose all effectiveness.
Women in need of emergency contraception do have another option, however: the copper IUD (Paragard).
IUDs are intrauterine devices that not only are considered 99.9 percent effective for emergency contraception, but they can remain in place for up to 10 years and are one of the most effective forms of contraception overall. While in the past doctors may have been reluctant to provide IUDs for younger women and women who have not had children, more current research suggests that their concerns about side effects were largely unfounded.
Copper IUDs work to prevent pregnancy by inhibiting fertilization, primarily by preventing sperm from reaching an egg. They may also help to prevent implantation of a fertilized egg, but they do not interfere with an established pregnancy. (It is important to remember that IUDs do not protect against HIV or other sexually transmitted infections, so barrier methods may be needed as well for protection.)
For more information, read more about the safety of prescribing the IUD for teenagers, along with this post on the pros and cons of IUDs. For more information on EC, see the Princeton/ARHP emergency contraception website.