Does Plan B Always Work? Emergency Contraception, Explained

• Plan B (levonorgestrel 1.5 mg) is highly effective but not 100% — it works mainly by delaying ovulation, so it can fail if ovulation has already happened.
• Sooner is better. Take levonorgestrel within 72 hours (ideally within 24); ulipristal works up to 120 hours; a copper IUD works up to 120 hours and is over 99% effective.
• EC is NOT an abortion pill. It prevents pregnancy from starting and does not harm an established pregnancy — confirmed by WHO, ACOG, FOGSI and ICMR.
• If you weigh over 75–80 kg or are near ovulation, ulipristal or a copper IUD is more reliable than levonorgestrel.
• Take a pregnancy test if your period is more than a week late, around 3 weeks after the unprotected sex.
• EC is a backup, not a routine method — frequent need is a signal to switch to reliable regular contraception.

"Plan B" is the global brand name for levonorgestrel 1.5 mg taken as a single tablet. In India the same medicine is sold as i-Pill, Unwanted 72, Pill 72 and other brands. Levonorgestrel is a synthetic progestin used safely in contraception for decades.

Its main job is simple: delay or prevent ovulation. When you take it before your body releases the hormone surge (the LH surge) that triggers What Ovulation Actually Means, it pushes ovulation back by several days. By the time an egg is released, the sperm from the earlier sex have died (sperm survive up to 5 days, usually 2–3). No egg meets sperm, so no pregnancy starts.

This is why timing relative to your cycle matters more than the clock. EC works best before ovulation and barely works once ovulation has already happened — and most people cannot know the exact moment they ovulate without tracking cervical mucus or using ovulation tests.

Just as important is what EC does not do. It does not end an existing pregnancy and does not work as an abortion pill. The older idea that it works by blocking implantation is no longer supported by evidence. WHO, ACOG, FOGSI and ICMR all confirm levonorgestrel EC is not an abortifacient — a reassuring fact if you ever continue a pregnancy that EC did not prevent.

• Levonorgestrel pill (i-Pill, Unwanted 72, Pill 72): The most accessible — over the counter, no prescription, Rs 60–150. Works up to 72 hours, best within 24. Right for most situations.
• Ulipristal acetate (ellaOne): A selective progesterone receptor modulator that can delay ovulation even after the LH surge has begun — something levonorgestrel cannot do. Works up to 120 hours and is more effective near ovulation. Less widely stocked; Rs 500–1,500.
• Copper IUD (Cu-T 380A): Inserted within 120 hours, it is over 99% effective — far more reliable than any pill — and keeps working as long-term contraception. The trade-off is needing a same-day clinic visit.

• Within 24 hours: ~89% of expected pregnancies prevented
• Around 48 hours: ~75%
• Around 72 hours: ~58%
• After 72 hours: levonorgestrel is no longer recommended — use ulipristal or a copper IUD

• Within 24 hours: Any option works. Levonorgestrel is the easiest — take it immediately.
• 24–72 hours: Levonorgestrel still works but is declining; ulipristal is more effective; a copper IUD remains over 99% effective.
• 72–120 hours: Levonorgestrel is no longer recommended. Choose ulipristal (ellaOne) or a copper IUD.
• Beyond 120 hours (5 days): Oral EC no longer works. A copper IUD may still be used up to 5–7 days in some cases. Otherwise, test for pregnancy in 3 weeks.
• Near ovulation (highest-risk days): Ulipristal or a copper IUD is more reliable. If neither is available, still take levonorgestrel — partial protection beats none.
• Just before your period (lowest-risk days): EC may not be needed, but if your cycles are irregular or you are unsure, take it anyway — it does no harm.

• Nausea (about 15–25%) — take EC with food or at bedtime; if you vomit within 3 hours, repeat the dose
• Mild headache, fatigue, breast tenderness, or light cramping — usually settle within 24 hours
• Spotting in the days afterward — common and harmless
• Changes to your next period — it may come a few days early or late (up to a week either way) and be heavier or lighter than usual; the cycle after that is usually back to normal

EC sometimes fails, and the most common reasons are predictable: it was taken after ovulation had already happened, body weight reduced its effect, vomiting within 3 hours lowered absorption, a drug interaction interfered, or there was further unprotected sex after the dose (EC only covers the past act, never future ones).

Also remember what EC cannot do: it gives no protection against sexually transmitted infections. If the unprotected sex involved a new or untested partner, plan STI testing alongside EC — our guide to STI screening for Indian women covers the free NACO services and timing for each test.

If a pregnancy is confirmed and not wanted, India's law allows legal termination at registered centres up to 20 weeks for any indication (and 24 weeks for specific categories). Medical abortion with mifepristone and misoprostol is the standard early option — free at government facilities, Rs 1,500–5,000 privately.

• Condom broke during sex: Take levonorgestrel as soon as possible (within 24 hours is ideal). Continue any other method as normal and test in 3 weeks if your period is late.
• Missed two or more active pills, then had sex: Take the most recent missed pill, take EC, continue the pack, and use barrier backup for 7 days.
• Used withdrawal and partner didn't pull out in time: Take EC — pre-ejaculate can carry sperm, as explained in our guide to whether precum can cause pregnancy.
• Realised 3 days later: You're at the edge of levonorgestrel's window (~58%). Prefer ulipristal or a copper IUD if you can; otherwise take levonorgestrel.
• 4–5 days later: Levonorgestrel is no longer recommended — use ulipristal or a copper IUD within 120 hours.
• Took EC, then had more unprotected sex: That's a separate event needing its own EC. The clearer fix is starting reliable regular contraception now.
• Reaching for EC several times a year: It's safe, but far less reliable than a regular method. Book a contraception review.

Used occasionally, EC is one of the best safety nets in reproductive health. But it is meaningfully less effective than regular contraception — the levonorgestrel pill prevents 58–89% of expected pregnancies, while IUDs and the daily pill are far more reliable across a year of use.

Relying on EC repeatedly also adds up in cost, side effects and cycle disruption — and usually points to an underlying gap: a condom that keeps failing, pills that are often missed, or no regular method at all. If condom failure is the issue, our guide to how effective condoms really are helps; if you've just had a baby, see postpartum contraception in India.

If you find yourself needing EC more than two or three times a year, treat it as a signal to switch methods — a low-maintenance, set-and-forget option (IUD, implant or injection) transforms the experience for many people.

• Severe, one-sided lower abdominal pain, shoulder-tip pain, faintness or unusual bleeding — these can signal an ectopic pregnancy and need same-day evaluation (EC does not cause ectopic pregnancy, but any pregnancy can be ectopic)
• You vomited twice within 3 hours of the dose and are unsure it was absorbed
• Your period is more than a week late despite a negative pregnancy test
• You take rifampicin, anti-epilepsy medicines or St John's wort and need EC — ask about a copper IUD or a doubled dose
• You've needed EC several times this year and want a more reliable plan
• There was possible STI exposure and you need screening and, if relevant, HIV prevention advice

• WHO — Emergency contraception (fact sheet)
• ACOG — Emergency Contraception (Practice Bulletin / patient FAQ)
• FOGSI — Family planning and contraception resources
• NHS — Emergency contraception (morning after pill, IUD)
• Ministry of Health & Family Welfare, India — The Medical Termination of Pregnancy (Amendment) Act, 2021