How Long Does Plan B Last?

Using Plan B to Prevent Pregnancy When Plan A Fails

Having unprotected sex is obviously not a good idea when you don't want to become pregnant, but sometimes the first line of defense fails or circumstances beyond your control leave you at risk for an unplanned pregnancy. Whether the condom broke, you forgot to take your birth control pill or you had unprotected sex, an emergency contraceptive like Plan B can help to prevent pregnancy.

What Is Plan B and How Does It Work?

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Plan B is the brand name for an emergency oral contraceptive designed to prevent pregnancy after unprotected sex, which is why it is also knows as the morning-after pill. Using a synthetic form of the hormone progesterone called levonorgestrel, Plan B prevents pregnancy by interfering with fertilization and implantation. The hormone delays ovulation so that sperm cannot reach an egg to fertilize it. It also irritates the uterine lining to make implantation less likely in the event that sperm and egg do meet.

Where Can You Get Plan B, and How Effective Is It?

Unlike regular birth control pills that require a doctor’s prescription, Plan B is available over-the-counter at any pharmacy. Timing is of the essence when using Plan B: The sooner you take it after unprotected sex, the more effective it will be. Plan B will continue working in the body for up to five days, but it is only 89 percent effective at preventing pregnancy if taken within three days of unprotected sex.

If you are overweight, Plan B may not work for you, because it is less effective for women with a BMI above 25. It will also fail to work if your body has already begun the ovulation process when you take it.

Can I Use Plan B in Lieu of Regular Birth Control?

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Plan B got its name because it was intended as a backup plan rather than a go-to contraceptive. Long-term use of Plan B is not recommended. While it is easier than regular birth control pills because you only have to take one pill, Plan B is more expensive and less effective than traditional birth control pills.

Side Effects Associated With Plan B

As with any other substance you might consume, Plan B does have side effects. After taking Plan B, you may experience nausea, vomiting, cramping and irregular bleeding. Fortunately, the side effects of Plan B are typically mild.