Are You Getting That Particular Drug Because You Need It Or Because Your Doctor Has Unwittingly Been Bribed By A Drug Company?
I write in "Good Manners for Nice People Who Sometimes Say F*ck" about research by psych prof Dennis Regan that suggests that giving someone even a small gift triggers our psychological mechanism for reciprocity:

Participants were told it was research on art appreciation. The actual study--on the psychological effects of having a favor done--took place during the breaks between the series of questions about art. Regan's research assistant, posing as a study participant, left the room during the break. He'd either come back with two Cokes-- one for himself and one he gave to the other participant--or come back empty-handed (the control group condition).

After all the art questions were completed, the research assistant posing as a participant asked the other participant a favor, explaining that he was selling raffle tickets and that he'd win a much-needed $50 prize if he sold the most. He added that any purchase "would help" but "the more the better." Well, "the more" and "the better" is exactly what he got from the subjects he'd given the Coke, who ended up buying twice as many tickets as those who'd gotten nothing from him.

Regan's results have been replicated many times since, in the lab and out, by Hare Krishnas, who saw a marked increase in donations when they gave out a flower, book, or magazine before asking for money; by organizations whose fund-raising letters pull in far more money when they include a small gift, like personalized address labels...

Unfortunately, it's not so benign when it happens in a medical situation.

Charles Ornstein reports at NPR that whether a drug company rep buys your doctor lunch makes a difference in whether you get prescribed their pricey, brand-name drug:

Evidence is mounting that doctors who receive as little as one meal from a drug company tend to prescribe more expensive, brand-name medications for common ailments than those who don't.

A study published online Monday by JAMA Internal Medicine found significant evidence that doctors who received meals tied to specific drugs prescribed a higher proportion of those products than their peers. And the more meals they received, the greater share of those drugs they tended to prescribe relative to other medications in the same category.

The researchers did not determine whether there was a cause-and-effect relationship between payments and prescribing, a far more difficult proposition, but their study adds to a growing pile of research documenting a link between the two.

A few examples:

Physicians who received meals related to Crestor on four or more days prescribed the cholesterol-fighting drug at almost twice the rate of doctors who received no meals. The difference was even more marked for the other drugs. Physicians who received meals prescribed Bystolic, a blood pressure pill, at more than five times the rate of their uncompensated peers; Benicar, for high blood pressure, at a rate 4.5 times higher; and Pristiq at a rate 3.4 times higher.

Higher rates of prescribing were also observed when doctors received just a single meal, even after taking into account a physician's specialty and region of practice.

Dr. R. Adams Dudley, a professor of medicine and health policy at UCSF and one of the study's authors, said he and his colleagues expected to see "some evidence that doctors were responsive to incentives, what with their being humans and all."

Still, he said, "I think we were probably surprised that it took so little of a signal and such a low-value meal. ... It has changed our thinking."

Here's a good question:

In an editor's note, Dr. Robert Steinbrook wrote that the recent analyses "raise a broader question. Is it necessary to prove a causal relationship between industry payments to physicians and the prescribing of brand-name medications?"

Other than for research and development, and related consulting, Steinbrook wrote, "it is already evident that there are few reasons for physicians to have financial associations with industry. Outright gifts, such as meals, may be legal, but why should physicians either expect or accept them?"