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BETHESDA, Md. (WUSA9) -- Concerns about the most widely used emergency contraceptive pill tops our health alert.

We are talking about a pill known as "plan B". New research shows the medication is not as effective as once thought. It isprompting a review from the Food and Drug Administration.

European authorities put new warning labels on a drug called Norlevo. It is identical to the "plan B" pill here in the United States. The drug is shown to lose effectiveness in women starting at around 165 pounds

Kathryn I. Marko, MD of George Washington University Medical Faculty Associates says,"It really becomes ineffective at 175 pounds which even in a woman that is very tall could be normal BMI but could potentially not have an effect for this particular type of emergency contraception."

At this point, the information is not on the packaging for plan B. So the FDA is looking at data to consider adding a warning about the effectiveness of the pill. Dr. Marko says there are other alternatives that don't lose effectiveness. So if you are considering using emergency contraception, you should talk to a physician.

"People are taking this to avoid unintended pregnancy and so if they do have an unintended pregnancy after taking emergency contraception and believing that it's going to work it would be really devastating for the person," adds Dr. Marko.

Earlier this year, the active ingredient in Plan B was approved to be sold over-the-counter without age restrictions.