Ella and Plan B are both emergency contraceptive pills, but they are not equally effective in every situation. Within the first three days after unprotected sex, they perform similarly. After that point, ella maintains its effectiveness through day five while Plan B’s reliability drops off. Your weight, timing, and whether you use hormonal birth control all factor into which one works better for you.
How Timing Affects Each Pill
Both ella and Plan B work by delaying or preventing ovulation, but the window of reliable protection differs between them. For the first 72 hours (three days) after unprotected sex, the two pills reduce pregnancy risk at comparable rates. The real difference shows up on days three through five.
Ella continues to lower pregnancy rates consistently through the full 120-hour (five-day) window. Plan B still offers some protection during days four and five, but pregnancy rates climb noticeably after the three-day mark. A large analysis of Plan B found that pregnancy rates stayed low through day four but increased at four to five days. If you’re past the 72-hour mark, ella is the stronger option.
That said, both pills work best the sooner you take them. Waiting even a few extra hours reduces effectiveness for either option. If you have access to Plan B right now but would need to wait until tomorrow to get a prescription for ella, taking Plan B sooner could be the better practical choice, especially within that first three-day window.
Why Body Weight Matters
Plan B becomes less effective at higher body weights. The CDC notes that people with a BMI of 30 or above have a higher risk of pregnancy after taking Plan B compared to those with a BMI under 25. The active ingredient in Plan B, a type of progestin, is particularly sensitive to weight and BMI.
Ella may also be somewhat affected by higher body weight, but the evidence is less clear, and the effect appears smaller. Research from Oregon Health & Science University found that ella is likely the better emergency contraceptive option for people with a higher BMI. If your BMI is 30 or above, ella or a copper IUD (which works regardless of weight) are worth discussing with a provider.
How to Get Each One
Plan B is available over the counter at pharmacies, grocery stores, and online with no age restriction and no prescription needed. You can walk in and buy it off the shelf. Ella requires a prescription, which means you’ll need to contact a healthcare provider, either in person or through a telehealth service. Some online platforms can prescribe and ship ella quickly, but there’s an inherent delay compared to grabbing Plan B at a nearby store.
This accessibility gap is one of the biggest practical differences between the two. Ella is the more effective option past 72 hours and for people at higher weights, but it’s harder to get in a time-sensitive situation.
Interaction With Hormonal Birth Control
This is a detail many people miss. If you’re planning to start or restart hormonal birth control (the pill, patch, ring, implant, or shot), the timing depends on which emergency contraceptive you took.
After taking Plan B, you can resume or begin hormonal birth control right away. After taking ella, the CDC recommends waiting at least five days before starting any hormonal method. Ella works by blocking a specific hormone receptor, and introducing additional hormones too soon can interfere with how it works. You should also avoid taking Plan B within five days of taking ella, since the two medications can counteract each other. Use a barrier method like condoms during that five-day gap.
Side Effects for Both Pills
The side effect profiles are similar. Both pills can cause nausea, and both can shift your next period, either making it arrive a few days early or a few days late. Some people experience headaches or fatigue. These effects are temporary and generally mild. If you vomit within a couple of hours of taking either pill, it may not have been fully absorbed, and you should contact a provider about whether to take another dose. Anti-nausea medication can help if you’re prone to stomach upset.
If your period is more than a week late or you experience unusually heavy bleeding, take a pregnancy test.
Using Emergency Contraception More Than Once
A systematic review published in BMJ Sexual & Reproductive Health found that the available evidence on repeated use within the same menstrual cycle is limited but does not suggest safety concerns. Studies of ella found no serious adverse events even at multiple doses per month, and studies of Plan B showed no differences in pregnancy or infant outcomes at higher cumulative doses.
One finding worth noting: among people who became pregnant despite using Plan B in that cycle, those who had used it multiple times had roughly 2.5 times the odds of an ectopic pregnancy (where the embryo implants outside the uterus) compared to single-use cases. This doesn’t mean repeated use causes ectopic pregnancies, but it’s a signal that deserves attention.
Emergency contraception is safe to use more than once, but it’s less effective than ongoing birth control methods. If you find yourself needing it frequently, a longer-term method will give you more reliable protection.
Breastfeeding Considerations
Plan B is generally considered compatible with breastfeeding. Ella is different: the FDA recommends against its use by breastfeeding women because its effects on infants through breast milk haven’t been studied well enough to rule out risk. If you’re nursing and need emergency contraception, Plan B or a copper IUD are the typical recommendations.
Quick Comparison
- Effective window: Plan B works best within 72 hours; ella works well through 120 hours.
- At higher body weight: Ella is likely more effective; Plan B’s reliability drops at a BMI of 30 or above.
- Access: Plan B is over the counter; ella requires a prescription.
- With hormonal birth control: Plan B has no waiting period; ella requires a five-day gap before starting hormonal methods.
- Breastfeeding: Plan B is considered safe; ella is not recommended.
- Cost: Plan B typically runs $20 to $50 at a pharmacy; ella is often similar in price but may involve a consultation fee for the prescription.