You may be taking prescription drugs that affect your driving but not be aware you are putting yourself and others at risk, says research published in the Journal of Studies on Alcohol and Drugs.

Almost 20 percent of people surveyed said they used a prescription drug with the potential for impairment, but some weren't aware that it could affect their driving, even though they may have been warned by their doctor or pharmacist.

The study, which was the first of its kind, found that the percentages of those who said they had received a warning from one of those sources varied by type of medication: 86 percent for sedatives, 85 percent for narcotics, 58 percent for stimulants, and 63 percent for antidepressants.

"We were very surprised that our study was the first we could find on this topic," says lead researcher Robin Pollini of the Injury Control Research Center at West Virginia University. "It's a pretty understudied area, and prescription drugs are a growing concern."

The study found that the type of medication in question was also related to drivers' perceptions about their impairment risk. They were most likely to think that sleep aids were the most likely to affect safe driving, followed by morphine/codeine, other amphetamines, and muscle relaxants.

Attention-deficit hyperactivity disorder (ADHD) medications were viewed as least likely to affect driving risk, while sleeping aids were viewed as the most likely to cause an accident or result in criminal charges.

Pollini says she hopes this research will lead to increased warnings provided by doctors and pharmacists, as well as improved labeling for medications that are likely to impair driving.

"The vast majority of drivers who are recent users of prescription drugs that have the potential for impairment have come into contact with a physician, a pharmacist, and a medication label," says Pollini.

"There's an opportunity here that's not being leveraged: to provide people with accurate information about what risks are associated with those drugs," she continued. "People can then make informed decisions about whether they're able to drive."

A study earlier this year released by the Governors Highway Safety Association and the Foundation for Advancing Alcohol Responsibility found that drivers killed in automobile accidents were more likely to be on drugs than drunk.  The study found that 43 percent of drivers in fatal 2015 accidents had used a legal or illegal drug.