The Morning-After Pill Doesn’t Work for Every Body — Three Things You Need to Know

By Kendall @ Planned Parenthood | Feb. 22, 2023, 10:03 p.m.

Many people know that emergency contraception, often called the morning-after pill, can help prevent pregnancy after sex — maybe the condom broke, you forgot to use protection, or there was an oopsie with your birth control. Not to be confused with abortion pills that end an early pregnancy, morning-after pills prevent pregnancy BEFORE it even begins.

But what you might not know is that some morning-after pills may not be effective for the average-sized American. Surprising factors like your weight and medicines you’re taking can affect how well it works.

Here’s what to think about when picking the best type of emergency contraception for you:

Weigh your options

If you weigh more than 165 pounds, Plan B and other over-the-counter levonorgestrel pills may not work. But there’s another type of morning-after pill called ella, available by prescription, that you can use.
If you weigh 195 pounds or more, ella is less effective.
No matter how much you weigh, you still have other options: You can get a copper or hormonal IUD up to five days after unprotected sex to prevent pregnancy.

Scientists aren’t sure why weight affects the effectiveness of the morning-after pill, but they’re working on figuring it out. The average woman in the U.S. is 170 pounds, and it’s just plain wrong that a common and essential medicine may not work for most of the people who need it.

It's about time

Technically the morning-after pill can be taken within five days of unprotected sex. But as time passes, it gets less effective, especially for levonorgestrel pills like Plan B. So it’s best to take it as soon as you can. If more than three days have passed since you had unprotected sex, ella is a better option.

Morning-after pills work by temporarily stopping your ovary from releasing an egg until any sperm in your body dies, which takes about five days. It’s kind of like pulling the emergency break on ovulation. But you have to take the morning-after pill before you start ovulating, otherwise it won’t work — that’s why it’s important to act quickly.

Learn more about when to take emergency contraception.

Some medicines can lower the effectiveness of morning-after pills

Medicines that can affect how well both ella and levonorgestrel pills like Plan B work include:

The antibiotic Rifampin (other antibiotics are fine)
The antifungal Griseofulvin (other antifungals are fine)
Certain HIV medicines
Certain anti-seizure medicines, sometimes also used to treat psychiatric disorders like bipolar disorder
The herb St. John’s wort

Contact the expert, supportive medical staff at your local Planned Parenthood health center for all of your questions about emergency contraception and other methods of birth control. You can also talk with a live sex educator on our free and confidential chat/text line.

This quiz can help you figure out the best emergency contraception for you.

Tags: birth control, emergency contraception, the morning-after pill