The results of the study show that 11 percent of women ages 15 to 44 say they've used the morning-after pill. That's up from 4 percent in 2002, which is only a few years after the pills went on the market and adults still needed a prescription.
Half the women said they did it because they'd had unprotected sex. Others said they were worried the birth control method they used had failed.
The study also found white women and more educated women use the morning-after pill the most.
Experts believe the increased popularity is likely because it is easier to get now and because of media coverage of controversial efforts to lift the age limit for over-the-counter sales. A prescription is still required for those younger than 17 so it is still sold from behind pharmacy counters.
The morning-after pill is basically a high-dose version of birth control pills. It prevents ovulation and needs to be taken within a few days after sex. The morning-after pill is different from the so-called abortion pill, which is designed to terminate a pregnancy.
At least five versions of the morning-after pills are sold in the United States. They cost around $35 to $60 a dose at a pharmacy, depending on the brand.
The results of the study were released Thursday by the Centers for Disease Control and Prevention. It's based on interviews of more than 12,000 women in 2006 through 2010.
Here are other findings from the study:
- Among different age groups, women in their early 20s were more likely to have taken a morning-after pill. About 1 in 4 did.
- About 1 in 5 never-married women had taken a morning-after pill, compared to just 1 in 20 married women.
- Of the women who used the pill, 59 percent said they had done it only once, 24 percent said twice, and 17 percent said three or more times.
The Associated Press contributed to this report.