Plan B vs ella: Emergency Contraception Timing, Effectiveness & Access

Quick Answer: Plan B One-Step (levonorgestrel 1.5 mg) is available over the counter without age restrictions; its label says to take it as soon as possible within 72 hours of unprotected sex. ella (ulipristal acetate 30 mg) requires a prescription and is labeled for use within 120 hours (5 days). In a randomized trial of more than 1,600 women (Glasier 2010), ella had a lower pregnancy rate, and in a pooled analysis its advantage was statistically significant within 72 hours. After ella, its label says to wait 5 days before starting or resuming hormonal birth control. A copper IUD placed within 5 days is the most effective emergency contraception. None of these protect against STIs, and none end an existing pregnancy.

Plan B vs ella at a Glance

Feature	Plan B One-Step	ella
Active ingredient	Levonorgestrel 1.5 mg (a progestin)	Ulipristal acetate 30 mg (progesterone receptor modulator)
Access	OTC, no age limit or ID	Prescription (including telehealth)
Labeled window	As soon as possible, within 72 hours	As soon as possible, within 120 hours (5 days)
Trial pregnancy rate, 0–72 h (Glasier 2010)	2.6%	1.8%
If you vomit	Within 2 hours: contact a health professional about repeating	Within 3 hours: consider repeating the dose
Restarting hormonal birth control	Can start right away; use backup per clinician advice	Wait 5 days; use a barrier method until next period
Main side effects	Headache, nausea, period changes	Headache, nausea, abdominal pain, period changes

Doses above are from the current U.S. Drug Facts or prescribing labels listed in Sources. Always follow the label on the package you buy, because store brands and formulations differ.

How Morning-After Pills Work

Emergency contraceptive pills reduce the chance of pregnancy after unprotected sex or a contraceptive failure, such as a broken condom or missed pills. Both work primarily by delaying or preventing ovulation, so sperm already in the reproductive tract cannot meet an egg. They do not work if you are already pregnant and they do not end a pregnancy; the Plan B label says not to use it if you are already pregnant because it will not work.

Levonorgestrel is a progestin that has been used in birth control pills for decades. Ulipristal acetate acts on the progesterone receptor and can delay ovulation even closer to the time an egg would be released, which is the leading explanation for why it performs better later in the window.

Timing: 72 Hours vs 120 Hours

The Plan B One-Step Drug Facts label says to take one tablet as soon as possible within 72 hours (3 days) after unprotected sex, adding that the sooner you take it, the better it works. The ella prescribing information says to take one tablet as soon as possible within 120 hours (5 days), at any time during the menstrual cycle, with or without food.

For both, sooner is better. If you are already past 3 days, ella or a copper IUD is the option designed for that window.

Effectiveness: What the Trials Show

Glasier and colleagues (Lancet, 2010) randomized women seeking emergency contraception to ulipristal acetate or levonorgestrel. Among 1,696 women treated within 72 hours, there were 15 pregnancies with ulipristal (1.8%) and 22 with levonorgestrel (2.6%); that difference alone was not statistically significant. In 203 women treated between 72 and 120 hours, all three pregnancies occurred in the levonorgestrel group. When the authors pooled this trial with an earlier one, pregnancies within 72 hours were 1.4% with ulipristal vs 2.2% with levonorgestrel, a statistically significant difference.

These percentages describe pregnancies among women who used the pills, not the chance of pregnancy after a single act of sex; many of those women would not have become pregnant anyway.

Does Body Weight Matter?

Some studies have found that emergency contraceptive pills, especially levonorgestrel, may be less effective in people with higher body weight or BMI, while other analyses have not shown a clear difference. The evidence is mixed. For that reason, clinicians sometimes suggest ella or a copper IUD, whose effectiveness is not thought to depend on weight, for people with higher weight. Importantly, no one should skip emergency contraception because of weight: taking a pill is still better than taking nothing.

The Most Effective Option: An IUD

The U.S. Office on Women’s Health lists the copper IUD, inserted by a health care provider within 5 days of unprotected sex, as the most effective type of emergency contraception, and it continues to provide ongoing birth control for years. An IUD requires a clinic visit, so it may not be practical for everyone within the time window.

Getting Each One

Plan B One-Step and generics (several brands contain the same 1.5 mg levonorgestrel) are on store shelves or behind the pharmacy counter, with no prescription, age limit or ID required. Generic versions contain the same active ingredient and dose.
ella requires a prescription from a clinician, which many people obtain through telehealth services, family planning clinics or, in some states, directly from a pharmacist. Because a pharmacy may need to order it, call ahead.

Some people keep a dose of emergency contraception at home so it is available immediately; check the expiration date.

Restarting Regular Birth Control

This is one of the most important practical differences. The ella label says to start or resume hormonal contraception no sooner than 5 days after taking ella and to use a reliable barrier method, such as condoms, until the next menstrual period, because hormonal contraceptives taken right away may reduce ella’s effect. After levonorgestrel, hormonal birth control can generally be started right away, with backup protection for a period your clinician or package insert specifies.

Neither pill provides protection for the rest of the cycle. Unprotected sex again after taking a pill can result in pregnancy.

Interactions and Cautions

The Plan B label says to ask a doctor or pharmacist before use if you take efavirenz (an HIV medicine), rifampin, or medicines for seizures, because these can reduce effectiveness.
The ella label also warns that drugs that strongly induce the liver enzyme CYP3A4 (such as some anticonvulsants, rifampin and St. John’s wort) may reduce its effectiveness.
Do not take ella and a levonorgestrel pill together or close together; they can counteract each other.
Breastfeeding: the ella label reports that small amounts of ulipristal pass into breast milk; discuss with a clinician. Levonorgestrel is generally considered compatible with breastfeeding.

What to Expect Afterward

Both pills can cause headache, nausea, fatigue, abdominal pain and changes in the timing of your next period. In the Glasier trial, headache was the most frequent adverse event, at similar rates in both groups (about 19%). If your period is more than a week late, take a pregnancy test. Seek care for severe lower abdominal pain, which could signal an ectopic pregnancy.

Common Questions and Misunderstandings

Not for regular birth control: the Plan B label says not to use it for regular birth control, and the ella label says it is not intended for routine use as a contraceptive. Ongoing methods such as pills, the patch, the ring, the shot, the implant or an IUD are far more effective than repeated emergency doses.
No STI protection: the Plan B label states it does not protect against HIV/AIDS or other sexually transmitted diseases. Consider STI testing after unprotected sex.
Only for sex that already happened: neither pill protects against unprotected sex later in the same cycle.
Allergy: the Plan B label says not to use it if you have ever had an allergic reaction to levonorgestrel.

When to Talk to Your Doctor or Pharmacist

Seek urgent care for severe lower abdominal pain 3 to 5 weeks after taking emergency contraception, which can signal an ectopic pregnancy. Take a pregnancy test if your period is more than 7 days late. Talk with a clinician about STI testing after unprotected sex, about an IUD if you want the most effective option, and about ongoing birth control.

Frequently Asked Questions

Is ella more effective than Plan B?

In the Glasier 2010 trial and a pooled analysis, ulipristal (ella) had fewer pregnancies than levonorgestrel, and only ella is labeled for use from 72 up to 120 hours after sex.

Do I need a prescription for ella?

Yes. ella is prescription-only in the US, though it can often be prescribed through telehealth. Plan B One-Step and its generics are OTC without age limits.

How long after sex can I take Plan B?

The label says as soon as possible within 72 hours. The sooner, the better it works.

Can I start birth control right after ella?

The ella label says to wait at least 5 days before starting or resuming hormonal birth control and to use a barrier method until your next period.

Will Plan B or ella cause an abortion?

No. They work mainly by delaying ovulation and do not work if you are already pregnant.

Does weight affect emergency contraception?

Some studies suggest pills, especially levonorgestrel, may be less effective at higher weight, but the evidence is mixed. A copper IUD is not affected by weight, and taking a pill is better than nothing.

Sources

Medical disclaimer: This article is for educational purposes and does not replace medical advice. Consult a licensed healthcare provider before starting any supplement, medication, or treatment — particularly if you are pregnant, breastfeeding, taking other medications, or have a diagnosed medical condition.