(Reuters Health) – Doctors who received even one free meal from a pharmaceutical salesperson were more likely than others to prescribe the drug being promoted, even when a generic equivalent was available, according to a new study.

Each year in the U.S., $73 billion is spent on brand name drugs for which there is an equivalent generic available, and patients pay for $24 billion of that amount themselves, said senior author Dr. R. Adams Dudley of the University of California, San Francisco.

“That’s an awful lot of money,” Dudley told Reuters Health by phone.

The brand name drugs and the generics are “so similar that there’s no benefit,” from using the brand name versions, he said.

Dudley’s team analyzed industry payment data from late 2013 and prescribing data for that year from doctors treating Medicare patients with common drugs for heart problems or depression.

For each class of drug, the researchers chose the most prescribed brand name. For the heart drugs, they chose Crestor (known generically as rosuvastatin) to represent the statins, Bystolic (nebivolol) for the beta-blockers, and Benicar (olmesartan) for angiotensin-converting enzyme inhibitors, or ACE inhibitors. They chose Pristiq (desvenlafaxine) to represent antidepressants known as selective serotonin and serotonin-norepinephrine reuptake inhibitors (SNRIs).

National organizations in the U.S. and U.K. have deemed these brand-name drugs to be no better than their generic forms, Dudley said.

Almost 280,000 doctors received a total of more than 60,000 payments associated with the four target drugs. The vast majority of the payments - 95 percent – were in the form of sponsored meals, on average less than $20 each.

Almost 9 percent of statin prescriptions were rosuvastatin. The other drugs in the study were prescribed less often.

But doctors who received even one sponsored meal from one of the pharmaceutical companies were more likely to prescribe the target drug over a generic alternative, compared to doctors who did not receive sponsored meals. As the number of meals and meal value increased, relative prescribing rates also increased, according to a report in JAMA Internal Medicine.

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“Payments for food and beverages are by the far the most frequent type of industry payments to physicians in the United States, totaling about $225 million in 2014, the most recent year for which data are available,” said Dr. Robert Steinbrook, an editor at JAMA Internal Medicine and a professor at Yale University School of Medicine.

“Recent research, including the new study being published in JAMA Internal Medicine, has convincingly shown an association between industry payments to physicians and the prescribing of brand-name drugs,” Steinbrook said by email.

A 30 day supply of rosuvastatin costs about $250, while a generic drug in the same class may cost $150 or less.

“You should ask your doctor, is there a generic that’s just as good whenever you start a new medicine,” Dudley said.

It’s not clear from this study whether receiving meals caused doctors to change their prescribing patterns, but “humans are very responsive to gifts,” he said. “Normal human behavior is reciprocity.”

Often a pharmaceutical salesperson will give a doctor a presentation about a new or existing drug and offer to do so over a free lunch, or snacks, and doctors are more likely to listen to their pitch if they can eat lunch at the same time, Dudley said. The salesperson then focus on the positive aspects of the drug they promote, rather than talking about how it has no benefit over generic.

This is sometimes a doctor’s only means of learning about new pharmaceutical developments, at least in the U.S., Dudley said.

“If we’re going to spend $75 billion on this, you can think of better educational approaches,” without commercial interest, he said.

Single-payer healthcare systems can negotiate the price of drugs, and negotiate lower prices for ones without proven benefit over existing options, Dudley said.

The American Medical Association limits physician “gifts” to $100 or less, and many academic medical centers now don’t allow drug reps on the premises.

“At UCSF they can’t even give us free samples, Kaiser doesn’t let drug reps in, for instance,” Dudley said. “Even without laws some organizations are responding.”

“(Pharmaceutical industry) promotional events are usually perfectly legal and acceptable to many physicians; otherwise physicians would not be attending,” Steinbrook told Reuters Health.

“But in the big picture, physicians have to ask themselves why they are accepting this largesse?” he said. “We should be advocating for drug and device manufacturers to spend less on promoting their products and more on independent bona fide research on safety, effectiveness and affordability.”