Morning after contraceptive Plan B has been found to be totally ineffective for women who weigh more than 176 pounds and somewhat ineffective for women over 165 pounds.

Left-leaning magazine Mother Jones reports the European version of the contraceptive, Norlevo, is changing its packaging to include the weight limit.

While this only officially applies to the European pill, American "morning after" pills are chemically the same as Norlevo and could have the same limitations.

The magazine notes research done by the Centers for Disease Control found similar results here in the U.S.  It also noted the weight of the average American woman over the age of 20 to be 166.2 pounds, meaning the pill will be ineffective for more than half of American women.

There is no word whether Teva Pharmaceutical, producer of Plan B: One Step, will put the warning on their "morning after" pills.

Plan B is considered the most effective "morning after" pill on the market and is available over the counter.