Summarize this article:

If you’ve had unprotected sex and are concerned that you could get pregnant, take the morning after pill, which is also called emergency contraception, as soon as you can. In most cases, you can take the morning after pill up to five days following unprotected sex.  Be aware that many states require women under the age of 17 to get a prescription for morning after pills.  You can take the pill anytime during your menstrual cycle.  The morning after pill is a safe and effective way to prevent pregnancy. However, you shouldn’t use this as a regular form of birth control. While everyone can use over the counter emergency contraception, it may not be as effective for every woman and some may be allergic to it. Make sure to read and understand any indications or contraindications that come along with emergency contraception.  The morning after pill may be less effective for women with a Body Mass Index (BMI) over 25.  Certain medications such as barbiturates, or other supplements such as St. John’s Wort may decrease the effectiveness of the morning after pill.  If you are allergic to any component of the morning after pill, it may be less effective. If you use any kind of morning after pill, you may experience some side effects. These usually subside after a few days.  You may experience nausea or vomiting after taking the morning after pill.  You may feel tired, dizzy, or have a headache after taking the morning after pill.  You may have breast tenderness, and lower abdominal pain or cramping after taking the morning after pill.  You may experience bleeding between periods or heavier menstrual cramps after taking the morning after pill.  Contact your doctor immediately if you experience bleeding or spotting that lasts longer than a week or if you have severe abdominal pain 3-5 weeks after taking the morning after pill. This can help rule out an ectopic pregnancy. One of the most common side effects of using emergency contraception is nausea. If you vomit within an hour of taking the pills, repeat the dosage.  Don’t repeat the entire process, just the dosage you threw up.  You may need to take an anti-nausea medication to help your stomach. Only use one form of emergency contraception. Not only is using two forms of emergency contraception not more effective at preventing pregnancy, but the different types of morning after pill may actually make the other less effective. You’re much more likely to have nausea, vomiting, and other side effects from using multiple forms of emergency contraception. If you’ve taken the morning after pill and don’t have a regular form of birth control, use a backup form of contraception. This can help prevent unwanted pregnancy.  Consider using condoms as your backup form of contraception.  Use backup contraception for 14 days after taking the morning after pill.

Summary:
Take emergency contraception as soon as possible. Talk to your pharmacist about indications. Watch for side effects. Repeat the dosage if you throw up. Avoid using multiple forms of emergency contraception. Use backup contraception.