There is no strict limit on how many times you can take Plan B in a week. The American College of Obstetricians and Gynecologists states that oral emergency contraception may be used more than once, even within the same menstrual cycle. That said, taking it repeatedly is a sign it shouldn’t be your go-to method, because it’s significantly less effective than regular birth control and will make your period unpredictable.
No Hard Cap, but Not Designed for Repeat Use
Plan B contains a single 1.5 mg dose of a synthetic hormone that works by delaying ovulation. It has a half-life of about 27.5 hours, meaning your body clears most of it within a couple of days. Taking a second or third dose in one week won’t cause a dangerous buildup, and there’s no medical guideline that says “never take it twice in seven days.”
What the packaging and every major medical organization will tell you is that Plan B is designed for occasional use. It’s a backup, not a strategy. If you’ve needed it more than once in a short window, that’s a practical signal to start or switch to a regular contraceptive method.
Side Effects Get More Noticeable
A single dose of Plan B causes mild side effects in most people. Common ones include nausea, fatigue, headaches, dizziness, breast tenderness, and abdominal cramping. These typically resolve within a few days.
The bigger issue with repeated doses is what happens to your menstrual cycle. Plan B can delay your period by up to a week and cause spotting or heavier bleeding between periods. Take it multiple times in a short span and your cycle can become genuinely confusing, making it harder to tell whether you’re late because of the hormone or because you’re pregnant. That uncertainty is one of the most practical reasons to avoid stacking doses.
It Won’t Hurt Your Fertility
A common worry is that frequent use could damage your ability to get pregnant later. The evidence is reassuring. A 2022 review in the journal Contraception found no increased risk of miscarriage, fetal abnormality, or child development problems after exposure to the hormone in Plan B. The review also found no indication that it disrupts normal menstrual cycles in the month following use. While no studies have tracked long-term fertility specifically after repeated emergency contraception, substantial evidence from other contraceptives containing the same hormone shows no impairment of future fertility, even after prolonged use. Repeated use of Plan B is unlikely to affect your ability to conceive down the road.
Each Dose Is Less Effective Than Regular Birth Control
The real cost of relying on Plan B isn’t health risk. It’s pregnancy risk. Plan B is 81 to 90 percent effective depending on how quickly you take it, with the best results coming in the first 24 hours (up to about 94 percent). Compare that to daily hormonal birth control, which is more than 99 percent effective when used properly. Every time you substitute Plan B for a regular method, you’re accepting meaningfully worse odds.
Timing matters a lot. The pill works best within the first 24 hours after unprotected sex and must be taken within 72 hours. After that window, effectiveness drops substantially. If you find yourself needing emergency contraception repeatedly, a copper IUD placed within five days of unprotected sex is 99 percent effective and then doubles as long-term birth control for years afterward.
Weight Can Reduce Effectiveness
Plan B becomes less effective at higher body weights. Research shows that the active hormone reaches significantly lower concentrations in the blood of women with obesity compared to women at a normal BMI. In one study, peak blood levels were about 35 percent lower in obese and extremely obese participants. The FDA hasn’t issued formal cutoffs for when the pill stops working, but if your BMI is above 30, a copper IUD or a prescription alternative called ella (which stays effective up to five days and works better across weight ranges) may be a stronger option.
What to Do If You’ve Taken It Twice This Week
If you’ve already taken Plan B more than once in the past few days, you’re not in medical danger. Watch for heavier-than-usual side effects like nausea or spotting, and expect your next period to arrive on an unusual schedule. If your period is more than a week late, take a pregnancy test.
Going forward, the most useful thing you can do is set up a regular contraceptive method. Options range from daily pills to patches, injections, implants, and IUDs, many of which are available at low or no cost through insurance or family planning clinics. Any of these will protect you far more reliably than keeping Plan B in your medicine cabinet as a routine backup.