According to federal data released on Thursday, use of emergency contraception rose after 2006, when access to the so-called "morning after" pill became easier for women.
The CDC reports that 11 percent of sexually active women used the morning after pill between 2006 and 2010, compared to just four percent in 2002. This report is the first by the government on emergency contraception since it became available without a prescription for adult women.
The morning after pill works by preventing ovulation in the days after unprotected sex, and some also believe that it makes the uterine lining less hospitable to a fertilized egg.
The CDC reports that 59 percent of women who used the morning after pill between 2006 and 2010 took it just once, while another 24 percent used it twice, and 17 percent used it three times or more.
Young adult women between the ages of 20 and 24 were the most likely to use the medication. One in four in this age group reported taking the morning after pill over a five year period.