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Doctors often cave in to patients' requests for brand-name prescription drugs even when generic versions are available, a new study suggests - a tendency that adds billions in costs for patients and the health system.

"This is, by definition, a wasteful expense," said the report's lead author, Eric Campbell, from Harvard Medical School in Boston.

"Doctors have the professional responsibility not to waste scarce medical resources," he told Reuters Health. "We have to educate doctors and patients about how wasteful this practice is."

The U.S. Food and Drug Administration requires generic drugs to be identical to their brand-name versions in active ingredients, dosage and strength. Generics are evaluated by the agency through a sped-up approval process once the patent on a brand-name medication has expired.

According to the FDA, the average generic drug costs 80 to 85 percent less than its brand-name version and the use of approved generics saved the U.S. $158 billion in 2010, for example.

On Campbell and his colleagues' survey, about four in ten of nearly 1,900 doctors across medical specialties said they sometimes or often prescribe brand-name drugs instead of a generic because their patient wants the branded version.

Doctors in smaller practices, as well as those who receive free samples or have so-called work lunches paid for by drug companies, were more likely to cave to patient requests for brand-name medications, according to findings published Monday in JAMA Internal Medicine.

The researchers also found internal medicine doctors and psychiatrists were more likely to agree to write prescriptions for brand-name pills over generic ones, compared to other specialists.

"Doctors today are very busy, and it may be that it's just easier to give in to these requests than spend a whole lot of time that they don't have" explaining why a generic is just as good, Campbell said.

But, he added, "This is not just doctors being bad - we have a system that's created to make sure that doctors are prescribing the expensive brands."

He pointed to free drug samples and meals from pharmaceutical companies as one of those system-wide drivers - and something states could crack down on if they wanted to cut prescription drug spending.

"Despite a growing recognition of the influence that pharmaceutical reps have on prescribing practices of physicians, and efforts by medical centers to limit that influence… the problem remains widespread," said Dr. Alex Federman from Mount Sinai School of Medicine in New York, who has studied generic drug use but wasn't involved in this study.

Television and magazine ads for various drugs also influence what patients ask their doctors for, Campbell added. Besides the U.S., the only other country that allows so-called direct-to-consumer advertising is New Zealand, according to the World Health Organization.

In another article published alongside Campbell's study, researchers led by Dr. Jonas Green from Cedars-Sinai Health System in Los Angeles looked specifically at cholesterol-lowering statins and found no evidence that branded versions are any better than generics.

Thus, the researchers write, "higher-priced statins are almost never clinically indicated."

Because statins are frequently used for many years, the drugs are one example of a case when prescribing generic instead of brand-name versions can lead to substantial savings for patients and for the health system over time.

Lipitor - a statin marketed by Pfizer, which is now available as a generic - is the best-selling medication in history, Green's team noted.

Prices vary widely, but Lipitor can cost $150 to $200 per month, depending on dose, compared to around $35 to $50 a month for the generic version of the drug, atorvastatin.

"With no good reason to use the higher-cost statins, there's nonetheless been more than $100 billion in branded statins prescribed in recent years, and there are much better ways to use that money," Green told Reuters Health.

For patients, he added, "Asking the question when prescribed a medication, ‘Is this generic, and if not, is there a generic version available?' can definitely open the door to things that may otherwise not come up in a conversation."

"Using a generic medication is a way to save money for yourself," Federman told Reuters Health in an email.

"I suggest that patients who are concerned about taking generics give the generics a try and if it doesn't work out the patient can always ask their physician to restart the brand name drug."