Excerpt from the full fact sheet:

Emergency contraception (EC), also known as the "morning-after" pill, is simply a concentrated dose of ordinary birth-control pills that can substantially reduce a woman's chance of becoming pregnant when taken within days of unprotected sex.  EC does not cause abortion; rather it prevents pregnancy by inhibiting ovulation, fertilization, or implantation before a pregnancy occurs.  EC is safe, effective, and simple to use and is not associated with any serious or harmful side effects.  EC is not dangerous to women with particular medical conditions, and women can diagnose their own need for the treatment.

Although EC has tremendous potential to help reduce unintended pregnancy, too few Americans are aware that contraceptive methods are available that can prevent pregnancy after sex.  In fact, only six percent of women aged 18 to 44 have used EC.  In order for EC’s full benefits to be realized, women must have broader access to it, they must use it correctly and consistently, and they must be educated about the medication’s availability and its effectiveness. 

Download the fact sheet (PDF)