This is troubling news, since the longer a woman has to wait to take the morning-after pill, the less effective it is.

If you find yourself needing emergency contraception—also known as the morning-after pill—you should be able to get it over the counter regardless of your age, thanks to a 2013 ruling by the U.S. Food and Drug Administration.

But many pharmacies aren’t following federal guidelines, according to a new study in the journal Women’s Health Issues. That's a problem, because it makes it more difficult for women to get the drug in time so it's still effective at preventing pregnancy.

For the study, researchers called 633 pharmacies throughout the state of Colorado, posing as potential customers and asking if and how emergency contraception (like brands Plan B One Step and Next Choice One Dose) is sold. The calls were all completed in mid-2014, after the FDA regulations had gone into effect.

“We know that Colorado has urban areas and frontier areas and rural areas, and we wanted to know if access would be different in different parts of the state,” says study co-author Carol Stamm, MD, associate professor of obstetrics and gynecology at the University of Colorado Anchutz.

What they found, however, were accessibility issues across the entire state. Overall, 87% of pharmacies reported having a product like Plan B, Next Choice, or a similar generic in stock. But of those that stocked the drugs, only 23% made them readily available on store shelves, without any restrictions or special requirements.

In 42% of stores that stocked the drugs, callers were told that the products were kept behind the counter and had to be requested from an employee. And in 56% of stores, callers were told that they’d need an ID or prescription to purchase the drugs.

Chain stores were significantly more likely to have emergency contraception in stock (90% versus only 58% of independent stores), and to have them readily available on store shelves (25% versus 10%). Pharmacies that were open 24 hours a day gave women the best chance at getting emergency contraception: All 20 round-the-clock stores surveyed had the drug in stock.

The study suggests that even if a store stocks emergency contraception, women might be told they’re not old enough to buy it or that they need a doctor’s approval—though there are no age restrictions and it doesn't require a prescription. This is not the only recent study to point out the accessibility problem, either.

So what's with the lack of access? The study authors say that pharmacy employees may be confused or misinformed about federal policies, and they point out that the age cutoff for emergency contraception changed four times in the years before it was lifted completely for Plan B in 2013 and for the drug’s generic versions in 2014.

But barriers to readily accessible emergency contraception—which can prevent pregnancy if taken soon enough after unprotected sex—can have real public health implications, says Dr. Stamm. “The more time elapsed before a woman takes the drug, the more its effectiveness decreases,” she says. “It’s good for up to five days, but it’s definitely going to work best in the first 24 hours. And if a woman is in a rural area and she can’t get it at one pharmacy, she may have to drive a long way.”

Even having emergency contraception behind the counter or locked in a display case can cause some women to think twice about purchasing it. “Now you have to tell a pharmacy employee that the condom broke or you had a contraception mishap, and that can be really embarrassing,” says Dr. Stamm.

The study was conducted more than three years ago, and Dr. Stamm hopes that accessibility has improved since then and that pharmacy staff are better informed about federal regulations. (Her team is working on another study to see whether educational interventions at certain pharmacies have improved matters, as well.)

But it’s likely that some women will still face opposition at the drugstore, she says, whether it’s an outdated store policy or an outspoken employee.

Based on the study’s findings, Dr. Stamm says that women who need emergency contraception will have the best luck at chain pharmacies. And for those who run into trouble trying to purchase it, “be persistent, choose another store, and go quickly,” she advises.

You can also ask your doctor about Ella, a newer form of emergency contraception that’s available via prescription and is sometimes covered by insurance. Ella can even be ordered online for next-day delivery after a brief online consultation. It may also be available at campus health clinics, Planned Parenthood facilities, hospital emergency departments, and urgent-care centers.