Less than half of young men have heard of emergency contraception, a recent study found, even though it’s available over the counter at drug stores and is effective at preventing pregnancy after sex.

The study, published in the March Journal of Adolescent Health, analyzed survey responses by 93 males ages 13 to 24 who visited the adolescent medicine clinic at Children’s Hospital Colorado in Aurora for a physical exam, illness or injury from August to October 2014. Most had been sexually active. The computerized survey asked patients about their knowledge of contraceptives, and whether they had talked about birth control with their partners or health care providers.

Although 84 percent of the teenage boys and young men said they believed avoiding pregnancy was very or somewhat important, only 42 percent had heard of emergency contraception, according to the study. Those who knew about emergency contraception were more likely to have talked with a health care provider about birth control in the past.

Far from being disappointed, Dr. Paritosh Kaul, an associate professor of pediatrics at the University of Colorado School of Medicine who co-authored the study, said he was “pleasantly surprised” at the 42%t figure.

“That’s two-fifths of the boys, and … we don’t talk to boys about emergency contraception that often,” he said. “The boys are listening, and health care providers need to talk to the boys.”

“These guys believe they should be involved in sexual health decision making,” Kaul said. “And if they are, then they’re more likely to talk with their girlfriends. They’re the missing half. It takes two to tango.”

If taken by women within five days of unprotected sex, emergency contraceptives can prevent ovulation, thus preventing pregnancy.

In 2013, the Food and Drug Administration approved one branded emergency contraceptive, Plan B One-Step, for sale over the counter.

without a prescription for all women. The next year, the agency said generic versions of the pills could also be sold over the counter without age restrictions.

Eighteen percent of sexually active women reported in 2013 that they had used emergency contraception sometime in the previous two years, according to the Centers for Disease Control and Prevention. That figure is probably higher now that the drugs are more readily available, said Kelly Cleland, a researcher at Princeton University who is executive director of the American Society for Emergency Contraception.

Although the Colorado study is too small to be the basis for generalizations, it’s one of the few studies that looks at awareness or access since emergency contraceptives became available over the counter, Cleland said.

She said her organization has received complaints from consumers who have been denied emergency contraceptives at the pharmacy, including men who have either been told that men can’t buy it or that they have to have the ID card of the woman for whom they’re buying it, neither of which is true, said Cleland.

Women can get emergency contraceptives at no charge under the health law, but only with a doctor’s prescription. For women who don’t take that step, sharing the cost, which can run up to $50, is one important way for men to play a role, Cleland said. “EC is so expensive when the burden falls on women exclusively.”