Roughly one in 10 teens are denied emergency contraception at pharmacies, new research claims.

Although these pills are legally available without a prescription for consumers of all ages, 10 percent of adolescents are incorrectly told they were too young to get them without a doctor's note.

Researchers also found pharmacists were more likely to provide the morning-after pill to teen boys than adolescent girls.

The study, led by researchers at Indiana University, illustrates how these barriers can lead to unintended teen pregnancies.

Researchers found one in 10 teens are wrongly denied emergency contraception at pharmacies

Emergency contraception, also known as the morning-after pill, can prevent pregnancy by stopping the ovary from releasing an egg, preventing sperm from fertilizing the egg or blocking the fertilized egg from implanting in the womb.

The drug works best when taken within 24 hours of unprotected sex or condom failure, although it can work for up to 72 hours.

'Emergency contraception works better the sooner you take it,' said lead study author Dr Tracey Wilkinson, a pediatrics researcher at the Indiana University School of Medicine in Indianapolis.

'Barriers to access can lead to delays in getting emergency contraception or prevent someone from getting it at all,' she added.

The US Food and Drug Administration initially cleared over-the-counter emergency contraception access for people age 18 and older, in part because of concerns about whether younger teen girls would use the medication properly.

The federal agency then lowered the age for non-prescription access to 17 before ultimately extending access to people of all ages in 2013.

For the study, Dr Wilkinson and her colleagues had mystery callers posing as physicians or teens call 993 retail pharmacies in five US cities.

Although four in five pharmacies said they had emergency contraception available for purchase that day, but roughly 1 in ten teens were wrongly told they were too young to get it without a prescription.

Researchers found that 11 percent of teen boys, eight percent of teen girls, and two percent of physicians calling on behalf of a young patient were incorrectly told they couldn't obtain emergency contraception because of age, researchers report in the Journal of Adolescent Health.

Only 52 percent of teen girls were correctly told they could get the morning-after pill without a prescription, compared to 62 percent of teen boys and 57 percent of female physicians.

The same group a researchers conducted a 'mystery shopper' study last year, wherein researchers posed as teenagers and went to pharmacies to ask for emergency contraception.

They found teens were often incorrectly told by pharmacies that they needed a prescription for the over-the-counter pill or they were denied it altogether because of their age.

Furthermore a 2012 study conducted by researchers at Boston University found that nearly 20 percent of pharmacists denied 17-year-old customers they could not purchase the drug because of their age.

One limitation of the current study is the possibility that what happens on the phone might not reflect what would happen in person.

Researchers also noted that it's not clear whether callers spoke to pharmacists or other staff at drugstores, and they lacked data to show whether emergency contraception was not provided due to an incorrect understanding of the law or a religious or moral objection.

Labels on the box may be part of the problem, said Dr Brian Nguyen, assistant program director of family planning at the Keck School of Medicine of the University of Southern California in Los Angeles.

Older packaging stated that emergency contraception was for women over 17, while newer labels are gender neutral and have no age restriction, Nguyen, who wasn't involved in the study, said by email.

Cost is an additional barrier.

'While emergency contraception may be over-the-counter, it is not free,' Nguyen said. 'Many adolescent health providers have adopted an evidence-based model of prescribing emergency contraception in advance so that the adolescent's insurance provider will cover the cost of the drug.'

Getting it ahead of time is the best way for teens to ensure they'll have access to emergency contraception when they need it, Dr Wilkinson said.

Parents can also discuss this option as part of a conversation about safe sex.

'I encourage all of my patients to have emergency contraception in advance of needing it and I prescribe it whenever I am prescribing birth control to ensure my patients have it,' Dr Wilkinson said. 'I also tell all patients – girls and boys – about emergency contraception and that they should be able to access it at a pharmacy.'