How Effective Is Plan B at Preventing Pregnancy
Plan B One Step and generic levonorgestrel pills are emergency contraceptives designed to reduce pregnancy risk after unprotected sex or contraceptive failure. When taken within 72 hours, Plan B lowers pregnancy risk by about 87% for average weight users, according to clinical data cited by the manufacturer and health agencies. The pill works primarily by delaying or preventing ovulation and is available without a prescription in most pharmacies and online stores. Real world effectiveness is lower than perfect use because timing, body weight, and existing ovulation affect outcomes. For people with a body mass index above 25 or weight over 165 pounds, efficacy drops, and a copper IUD or ulipristal acetate may be more reliable options read more on Planned Parenthood.
Timing, Weight, and Hormonal Interactions That Change Effectiveness
Effectiveness declines the longer you wait after unprotected sex. Taking Plan B within 24 hours is more effective than between 48 and 72 hours, and the drug is not recommended after 120 hours because evidence shows reduced benefit. Body weight and BMI matter: studies and guidance from the FDA and WHO note that levonorgestrel based pills may be less effective for people over roughly 165 pounds or with a BMI above 25. Certain medications can lower effectiveness by speeding metabolism of the hormone, including some anti seizure drugs, HIV treatments, and the herbal supplement St. John's Wort check FDA drug shortage updates. If you have already ovulated, Plan B is unlikely to work, which is why taking it as early as possible and confirming with a pregnancy test or clinician is important.
Plan B Compared With Other Emergency Contraception Options
Compared with ulipristal acetate, Plan B is less effective overall, especially closer to ovulation and for people with higher body weight. Ulipristal acetate can be taken up to 120 hours after unprotected sex and maintains higher efficacy in that window, but requires a prescription in many regions. The copper IUD is the most effective emergency contraceptive, with pregnancy rates below 1% when inserted within five days, and it provides ongoing reversible birth control see WHO contraception fact sheet. Plan B is widely available at pharmacies, campus health centers, and online retailers, and costs typically range from 40 to 50 dollars without insurance, though some plans cover it under preventive care mandates. For most people who take it promptly and fall within typical weight ranges, Plan B remains a practical, accessible option backed by decades of safety data and regulatory approval.