As many as 11 percent of women ages 15 to 44 who have ever had sexual intercourse have used a "morning-after" pill at least once, according to the first federal report on emergency contraception, released Thursday, USA TODAY reports. That's 5.8 million women -- half of whom said they used it because they feared their birth control method may have failed, and the rest who had unprotected sex. The National Center for Health Statistics analysis is based on responses collected through in-person interviews with 12,279 women from 2006 to 2010. Of those, 10,605 said they were sexually experienced. The report found that 23 percent of sexually experienced women ages 20 to 24 had ever used emergency contraception, compared with 16 percent ages 25 to 29, 14 percent ages 15 to 19 and 5 percent ages 30 to 44. Emergency contraception was most common among women 20 to 24, the never married, Hispanic and white women, and the college-educated.