You should use Plan B One-Step^® within 72 hours (3 days) after you've had unprotected sex or birth control failure to help prevent pregnancy from happening. The sooner you take it, the better it works.

Plan B One-Step^® is used as a backup emergency method for birth control if, for example:

• Your regular birth control failed (e.g., your partner's condom broke or slipped)
• You made a mistake with your regular method (e.g., you forgot to take your birth control pill)
• You didn't use any birth control method

Do not take Plan B One-Step^®:

• If you're already pregnant, because it won't work
• If you're allergic to levonorgestrel or any of the ingredients in Plan B One-Step^®
• In place of regular birth control. Plan B One-Step^® should not be used as routine birth control, as it isn't as effective
• To protect yourself from HIV infection (the virus that causes AIDS) or any other sexually transmitted diseases (STDs)

When taken as directed, Plan B One-Step^® is generally safe for women. Some women will have mild temporary side effects that include:

• Changes in your period
• Nausea
• Lower abdominal pain
• Fatigue
• Headache
• Dizziness
• Breast tenderness

These are similar to the side effects that some women have when taking regular birth control pills. Some women taking Plan B One-Step^® will have menstrual changes such as spotting or bleeding before their next period. Some women may have a heavier or lighter next period, or a period that is early or late. If your period is more than a week late, you should get a pregnancy test.

If you should experience severe abdominal pain, you may have an ectopic pregnancy and should get immediate medical attention.

The only way of knowing whether Plan B One-Step^® has worked is when you get your next period, which should come at the expected time or within a week of the expected time. If your period is more than one week late, you may be pregnant. If you have any questions or concerns, please be sure to call your physician or healthcare professional.

Keep in mind, Plan B One-Step^® is less likely to work if:

• You've already had unprotected sex or birth control failure earlier in your menstrual cycle
• You have unprotected sex or birth control failure again in the same menstrual cycle after taking Plan B One-Step^®
• You vomit within two hours of taking Plan B One-Step^® (talk to your healthcare professional if this happens)

If you're sexually active, it's always a good idea to see a healthcare professional for routine checkups. Your healthcare professional will talk to you about sexually transmitted diseases, and if necessary, test you for them, discuss effective methods of routine birth control, and answer any other questions you may have.