The effectiveness of morning after pills like Plan B One Step is liable to be much lower for women who weigh more than 165, with effectiveness dropping close to zero for anyone over 176.

Shocked? Maybe you shouldn’t be. The mechanism of action for emergency measures like Plan B is the same as it is for regular hormonal contraceptives. As bioanthropologist (and ladybusiness expert) Kate Clancy points out, it’s well known that regular birth control pills don’t work that well on people with BMIs over 25, so it’s likely that the lower efficacy of emergency contraceptives is something the pharmaceutical industry has known about for some time.

One possible solution: create different formulations for different women. “[The issue],” tweeted Clancy, “is [probably] that these pills don’t have enough hormone for some.”

Read more at Jezebel.