Recent news suggesting that the emergency contraceptive pill Plan B is ineffective for women who weigh more than 176 pounds came as a shock. How could the drug potentially fail so many women? 

The average American woman weighs about , which is not far from the point of diminishing success for Plan B. And 176 pounds might not be overweight or obese for many women, depending on factors such as height and BMI.

French drugmaker HRA Pharma found that levonorgestrel, one of the active ingredients in its brand of emergency contraception Norlevo, became less effective at preventing pregnancy in women who weighed 176 pounds or more. Levonorgestrel is also the active ingredient in Plan B, which is almost identical to Norlevo.

HRA Pharma is planning to change the drug's label to reflect the new findings, and the FDA is currently reviewing the research to determine whether the warnings should be applied to Plan B sold in the U.S. as well.

Physicians and the makers of the drug are quick to clarify that Plan B should only be used in emergencies when other birth control methods have failed, and not as a regular form of birth control.

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“Plan B is only considered about 80 percent effective in preventing pregnancy compared to routine birth control use that is typically 95 to 99 percent effective, depending on the method,” says Dr. Melissa Goist, an OB/GYN at Ohio State University’s Wexner Medical Center. “Certainly the timing of use and other factors (including timing of cycle and, potentially, users' weight) affect its efficacy."

Beyond Plan B: Long-Acting Birth Control

For those who want long-acting birth control, there are many options on the market, including patches, injections, intravaginal rings, and intrauterine devices (IUDs). Copper IUDs are seeing a resurgence in popularity in light of new studies, including one showing that they are safe for teenagers.

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An IUD remains one of the most fail-safe methods of birth control, regardless of a woman’s weight. However, the relatively high cost of the device and some religious opposition keep it from being feasible for some women.

Dr. Adam Jacobs, an associate professor of obstetrics, gynecology, and reproductive science at the Icahn School of Medicine at Mount Sinai Hospital, also says that having a reliable form of regular birth control is key. And standard oral contraceptive pills (OCPs) appear to be affective for women of all body types.

“There has been some debate over the issue of oral contraceptive pill efficacy and weight, but OCPs are still considered to be just as effective at any weight,” he says.

But what if you find yourself in an emergency?

“It is important to note that Plan B is probably the 'least effective' emergency contraceptive on the market,” Goist says. “The paragard IUD is most effective, if used within 5 days of intercourse, but needs to be inserted by a healthcare professional.”

Goist also suggests Ella, a newer form of emergency contraception that requires a prescription. However, it seems to diminish in effectiveness the closer a woman is to ovulation.