MILWAUKEE — More than a third of doctors said they prescribe brand name drugs simply because patients ask for them even when cheaper generics would be appropriate, according to a new study.

The practice, which can contribute to higher health care costs, was found to be more likely among doctors who received free drug samples or food from drug companies or who had financial relationships with drug companies.

“It is a classic measure of waste in medicine,” said lead author Eric Campbell, an associate professor at Harvard Medical School. The paper, published online Monday in JAMA Internal Medicine, involved a national survey of about 1,900 doctors from a variety of specialties.

A total of 37 percent of doctors said they sometimes or often prescribed brand name drugs if patients asked even if an equivalent generic was available.

If drug companies provided food or beverages at the workplace, 39 percent of doctors prescribed brand name drugs when patients asked, compared with 33 percent of doctors who did not get free food. If drug companies provided free drug samples, 40 percent of doctors prescribed brand name drugs, compared with 31 percent among those who did not get free samples.

Also, 40 percent of doctors who said they stayed up to date by meeting with drug company representatives prescribed brand name drugs over generics, compared with 34 percent of doctors who rarely or never met with drug reps.

The findings confirm what many people suspected, said Eric Cohen, a kidney specialist at the Medical College of Wisconsin and Froedtert Hospital.

“It makes perfect sense,” said Cohen, who was not a part of the study. “Even the smallest gift will sway someone's opinion. They (drug companies) don't do it out of the goodness of their heart.”

As a kidney specialist, Cohen said he often sees patients with pain who want the brand name painkiller Percocet instead of the generic equivalent.

Both drugs combine the opioid oxycodone with acetaminophen. But 30 tablets of the generic cost $52, compared with $217 for the brand name, he said.

Cohen and other doctors contacted for this story said consumer drug advertising, which began in the U.S. in 1997, is the main reason why doctors give in to patient demands and prescribe brand name drugs.

Only the U.S. and New Zealand allow such advertising, said Richard Deyo, a professor at Oregon Health and Science University.

Deyo said it is easier and faster for doctors to acquiesce to patients' demands for an advertised drug than to spend time explaining the disadvantages of doing so. That's especially true among doctors who don't want to alienate their patients, he said.

In a statement, the industry group that represents drug companies said many factors, not just patient demands, determine what drugs doctors prescribe. Those include clinical treatment guidelines, drug formularies, medical journal articles and doctors continuing medical education, said Matthew Bennett, a spokesman with the Pharmaceutical Research and Manufacturers of America.