MONDAY, March 26 (HealthDay News) -- Nearly one in five U.S. pharmacies gave out misinformation to researchers posing as 17-year-old girls seeking emergency contraception, often saying that it was "impossible" for girls to get the pill, a new study finds.

About 3 percent of researchers posing as physicians also received wrong information about the availability of emergency contraception, also known as the "morning-after" pill.

The findings show that 17-year-olds in need of emergency contraception to prevent unintended pregnancy face significant barriers in accessing it, the study authors said. According to U.S. federal regulations, girls 17 and older can buy emergency contraception without a prescription if they show proof of age, while girls 16 and younger need a doctor's prescription.

"What we found was that emergency contraception was pretty available, in that 80 percent had it on the shelf that day," said lead study author Dr. Tracey Wilkinson, a general pediatrics fellow at Boston University School of Medicine and Boston Medical Center. "However, when teenagers asked if they could get the medicine, they were [sometimes] told they couldn't get it at all, not with a prescription, not over-the-counter, just simply based on their age."

The study, published online March 26, appears in the April print issue of Pediatrics.

In the study, researchers called all the commercial pharmacies in five major U.S. cities: Austin, Texas; Cleveland; Nashville, Tenn.; Philadelphia; and Portland, Ore. Each of the 943 pharmacies got called twice, once by a "17-year-old girl" and once by a "physician." Researchers spoke to pharmacists, pharmacy technicians or unidentified pharmacy staff.

Four in five callers were told the pharmacy had emergency contraception in stock. However, 19 percent of 17-year-old callers were told that they could not obtain emergency contraception under any circumstances, while 3 percent of physicians were told their 17-year-old patient could not obtain it.

"Not just the callers posing as 17-year-olds, but the physicians were given wrong information by the pharmacy workers about over-the-counter access to emergency contraception," said Dr. Deborah Nucatola, an ob-gyn and senior director of medical services for Planned Parenthood Federation of America. "This kind of misinformation can result in preventable, unintended pregnancy."

About 85 percent of the roughly 750,000 teenage pregnancies in the United States each year are unintentional, the researchers noted.

Slightly more than half of workers in pharmacies that didn't have emergency contraception on hand said they could order the medication, but about one-third offered no additional information about how girls or doctors could get it. Also, the teen callers were put on hold more often than doctors and talked less often to pharmacists, the study found.

Researchers do not know if any pharmacy workers intentionally misled the girls, or if they simply don't know the law.

In 2011, the Center for Drug Evaluation and Research of the U.S. Food and Drug Administration (FDA) recommended that younger teens be permitted to obtain emergency contraception without a prescription, but that was overruled by the U.S. Secretary of Health and Human Services.

Emergency contraception is a high dose of progestin that prevents pregnancy by delaying ovulation (when the egg leaves the ovary and travels into the fallopian tube where it's available for fertilization by sperm). Some research suggests emergency contraception may make it more difficult for sperm to get past the cervix and into the uterus, and may make the uterus less hospitable to sperm.

Although the drug can be taken up to five days after unprotected sex, it becomes less effective the longer women wait. For every 12-hour delay in taking the first dose, the odds of pregnancy increase by 50 percent, according to background information in the study.

Emergency contraception is not an "abortive" drug, Wilkinson said. It does not affect an existing pregnancy or slow the transport of a fertilized egg from the fallopian tubes into the uterus, she said.

The average cost for emergency contraception was $45, ranging from $15 to $70.

Wilkinson added that emergency contraception should not be confused with RU-486 (mifepristone), which is used to terminate early pregnancies and is given by physicians under supervision.

To clear up the confusion, Wilkinson urged more education of pharmacy staff and said pediatricians and other health care workers must make sure that adolescents know their rights.

"Clinicians might help prepare their patients for this by writing a prescription as a backup to make sure they can access it when they need it," she said.

More information

Princeton University has more on emergency contraception.