REMINDER: if you have a vagina and want to use Plan B as an emergency contraceptive, it loses effectiveness if you weigh more than 165 lbs (74.84 kg) and is completely ineffective for those that weight more than 176 lbs (79.83 kg) (x)
Let me spread the shit out of this.
This is horrifying. And sadly true.
From what I’ve gathered, this has to do with the ability to metabolize levonorgestrel - the hormone in Plan B (and its generic derivatives). However, there are other options for emergency contraception if you are heavier than 176 lbs (or about 80kgs). The copper IUD (Paragard) and the ella (ulipristal acetate) are both effective for heavier women, and work if inserted/or taken within 5 days of unprotected sex. The Paragard is definitely a longer term option (and expensive), so it’s not what I’d recommend as a go to. The ella needs a prescription, (and you should check its availability at your pharmacy as it’s not always on hand) but it is still an excellent option for emergency contraception.