Seventeen-year-olds can legally buy Plan B over the counter at the drugstore, but nearly 20% of pharmacists incorrectly deny them access.

Related Pharmacies Deter Teens from Plan B, Study Shows MSNBC

About 1 in 5 pharmacies incorrectly denies teen girls access to emergency contraception (EC), or the “morning after pill,” according to a new study.

Posing as either 17-year-old girls or doctors seeking Plan B emergency contraception for their 17-year-old patients, researchers from Boston University called 943 drugstores — every pharmacy listed in five major U.S. cities. Eighty percent of the pharmacies said they stocked the drug.

By law, teenagers aged 17 and older can buy Plan B over the counter, but 19% of pharmacists told teenage callers they could not purchase it because of their age. Three percent of doctors were similarly told emergency contraception could not be given to 17-year-olds.

When asked whether they knew the legal age for Plan B access, only 57% of pharmacy employees answered correctly to teens; 61% answered correctly to doctors. Not surprisingly, teens were twice as likely as physicians to wait on hold, and four times less likely to be connected to a pharmacist to answer their questions.

Pharmacists were no more likely to provide correct information than non-pharmacists when speaking to physician callers.

“From our study, it appears that 1 in 5 adolescents who phone pharmacies looking for EC are told they cannot obtain it under any circumstances and that nearly half of all adolescents and physicians are told an erroneously high age for EC access without a prescription,” the authors write. “Such misinformation poses a potentially substantial barrier to access.”

MORE: U.S. Rejects FDA Advice to Sell Plan B One-Step Over the Counter

Earlier research by the same authors found that teens were more often misled about Plan B availability in low-income neighborhoods, where teen pregnancies are most common. In that study, while the same proportion of teens was given incorrect information overall, 24% of teens in low income areas were told the drug wasn’t available to 17-year-olds, compared with 15% of teens in more affluent neighborhoods.

It is not clear from the current study whether pharmacy employees deliberately misled teens to prevent them from getting Plan B or whether they were simply misinformed.

Late last year, the Obama administration provoked controversy when it rejected the Food and Drug Administration’s recommendation to remove the age restriction on Plan B completely. The FDA had reviewed the science on the drug’s effects and determined that it was safe for use in girls of all ages; however, Health and Human Services Secretary Kathleen Sebelius, in a surprising turn, overruled the agency’s decision to make the drug available for all.

Emergency contraception prevents pregnancy by inhibiting ovulation or by keeping an egg from becoming fertilized, but it is not effective if it is used more than 72 hours after sex and does not harm existing pregnancies.

The authors conclude: “[I]t appears from our study results that additional education regarding the current rules around EC dispensing is needed for pharmacy staff, adolescents, and physicians attempting to obtain this medication.”

The study was published in Pediatrics.

MORE: Subject for Debate: Are Women People?

Maia Szalavitz is a health writer for TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland‘s Facebook page and on Twitter at @TIMEHealthland.