The name of the game is to make “the healthy choice, the easy choice.” And we’re excited women can (finally) buy emergency contraception (EC) over the counter! More options, more resources, and removing barriers = awesome, right?!

Not so fast.

We talk about EC as a workable option for just about anyone who wants it. Seems easy enough. The problem is that research shows not all ECs are good for all female bodies. There are three kinds of EC we hear about in the U.S.: Levonorgestrel (LNG; i.e., Plan B, Next Plan, Postinor), ulipristal acetate (UPA; i.e., ella), and the copper IUD (i.e., Paragard):

• LNG is available over the counter without a prescription.
• UPA requires a prescription.
• The copper IUD must be inserted by a medical professional and accessibility varies widely among clinicians (sometimes taking several visits to be acquired and inserted).

As far as “patient friendly” goes, LNG may be the best choice with no doctor’s visit and no prescription. And everyone knows what Plan B is thanks to its sassy purple-hued commercials (brand recognition goes a long way—just ask teens how they feel about Trojan condoms over other brands). This is why in our field we keep the EC-talk simple: if you unprotected sex within this timeframe, go get EC—the sooner the better!

What we don’t talk about is that LNG is not effective for women whose body mass index (BMI) is over 25. (Check out more information about BMI here.) Now, it’s true that BMI is a somewhat controversial measurement of health, but it’s one that was correlated with EC failure.

LNG works for women whose BMI is 25 and lower, UPA works for women whose BMI is 35 and lower (and can be taken up to 120 hours after unprotected sex—longer than LNG), and the copper IUD works for most women if it can be inserted soon enough after sex. The take away is that the research shows that once a woman’s BMI reaches 26 and above, LNG becomes so ineffective, it’s basically a placebo.

So what does this mean? It means a few things. First, the most accessible methods of EC don’t work for a large portion of Americans who might want to use it. Second, we need to wholly reconsider how we talk about EC being a safe and effective method to prevent pregnancy when other methods fail.

Our clients, our students, and our patients have a low tolerance for “bad” information and by removing the required prescription from Plan B, there’s not a good line of defense to make sure folks are getting a good back-up method. There’s no easy way to explain the intersection of sex, hormones, body composition, and family planning, so how will you talk to young people about handling EC?

(Note: The study found two other covariate of EC failure in addition to BMI: existing probability of conception and the occurrence of further acts of unprotected intercourse after using EC.)