Ella and Plan B are not the same medication. They contain different active ingredients, work through slightly different mechanisms, and have different time windows, access requirements, and effectiveness profiles. Both are emergency contraceptive pills designed to prevent pregnancy after unprotected sex, but the similarities largely stop there.
Different Active Ingredients
Plan B One-Step contains levonorgestrel, a synthetic form of progesterone that has been used in hormonal contraceptives for decades. Ella contains ulipristal acetate, which belongs to a different drug class altogether. Rather than mimicking progesterone the way Plan B does, ulipristal acetate blocks progesterone’s activity at its receptor. This distinction drives most of the practical differences between the two pills.
How Each One Prevents Pregnancy
Both pills work primarily by preventing or delaying ovulation. Neither one causes an abortion. But they accomplish this differently, and that matters for timing.
Plan B floods the body with a high dose of synthetic progesterone, which can suppress the hormonal surge that triggers the release of an egg. The catch is that once that surge has already started, Plan B loses its ability to intervene. Studies show that women who took Plan B at or after this hormonal surge had the same ovulation rates and conception rates as women who took nothing at all.
Ella, by blocking progesterone receptors, can delay ovulation even after the hormonal surge has begun. This gives it an advantage in the later part of the fertile window, when Plan B is essentially no longer working.
Time Windows for Each Pill
Plan B can be taken up to three days (72 hours) after unprotected sex, though it works best the sooner you take it. Ella extends that window to five days (120 hours) after unprotected sex. And unlike Plan B, Ella maintains relatively consistent effectiveness across that entire five-day window rather than declining sharply with each passing day.
How Body Weight Affects Effectiveness
This is one of the most important differences between the two, and one that often gets overlooked. Research from Oregon Health & Science University found that people with a BMI of 30 or higher experienced Plan B failure four times as often as those with a BMI under 25. Blood levels of levonorgestrel were about 50% lower in people with a BMI of 30 after taking a standard dose, which likely explains the drop in effectiveness. Doubling the dose of Plan B did not solve the problem.
Ella’s effectiveness also appears to decrease somewhat at higher body weights, but not nearly to the same degree. Researchers describe the evidence as less clear-cut for Ella, though it is likely the better option for people with a higher BMI. Some data suggests emergency contraception in general becomes less reliable above a BMI of 26, making this a factor worth considering when choosing between the two.
Getting Access
Plan B has been available over the counter without a prescription since 2006. You can buy it at most pharmacies, and there is no age restriction. Generic versions with the same active ingredient are also widely available and typically cost less.
Ella requires a prescription. You’ll need to see a healthcare provider or use a telehealth service to get it. This adds a step, but the longer effectiveness window and better performance at higher body weights can make it worth the extra effort, especially if more than two days have passed since unprotected sex.
Side Effects
The side effect profiles are similar. Both pills can cause nausea, and both can shift the timing of your next period. Your period may come a few days early or a few days late. These effects are temporary and resolve on their own within a cycle or two.
Restarting Hormonal Birth Control
Here’s where the two pills diverge in a way that catches many people off guard. After taking Plan B, you can start or continue your regular hormonal birth control right away. After taking Ella, you need to wait five full days before starting or restarting any hormonal contraceptive that contains progestin, which includes the pill, the patch, the ring, the shot, and the implant. Starting hormonal birth control too soon after Ella can reduce the effectiveness of both the emergency contraception and your regular method, since progestin and ulipristal acetate work against each other. You’ll also need to use a backup method like condoms for seven more days after restarting your hormonal contraceptive.
Using Them More Than Once
Plan B can be used multiple times in the same menstrual cycle if needed. The American College of Obstetricians and Gynecologists has endorsed repeated use, and studies have not found increased side effects with multiple doses in one cycle. For Ella, the answer is less certain. There is limited research on taking it more than once per cycle, though related research on daily doses of ulipristal for other conditions suggests it is safe and well tolerated. If you find yourself needing emergency contraception frequently, that’s a good signal to explore a more reliable ongoing method.
Which One to Choose
The right choice depends on your situation. Plan B is easier to access, requires no prescription, and works well when taken within the first 24 to 48 hours, particularly for people with a BMI under 25. Ella is the stronger option if three or more days have passed, if you have a higher BMI, or if you’re later in your fertile window. If time and access aren’t barriers, Ella is generally considered the more effective of the two across most scenarios.