How would you react if you learned that your doctor prescribed a more expensive drug rather than an equally effective but cheaper medication? You probably wouldn't like it, even if your insurance paid most of the cost.

Doctors are the target for a large share of the estimated $20 billion the pharmaceutical industry spends each year on marketing. These marketing costs add to the higher prices we all pay for drugs and medical devices.

Chances are that your doctor does have some kind of relationship with industry, according to the results of a survey just published in the New England Journal of Medicine.

Almost all of the 1,700 doctors who answered the survey reported some form of contact with representatives from companies selling drugs or devices.

For example, 85 percent of them said they had received free food and drinks at company-sponsored lunches being held to describe their products.

Companies defend these and other practices as a legitimate way to educate physicians. And drug companies do help keep doctors abreast of the latest findings by reimbursing some of the expenses doctors incur while attending educational meetings.

For example, 35 percent of the physicians surveyed said that companies had reimbursed these costs. And 28 percent reported that drug companies had paid them for lectures they gave to medical audiences.

The problem is, there's no way to tell if the doctors delivering these educational lectures — as well as those listening — will be biased in favor of the products sold by the company that's paying their honorarium or inviting them to lunch.

I have given many such lectures that were sponsored by drug companies. I believe I was conveying valuable information to my audiences, and I always tried my best to be fair to the various competing products.

Even so, the content of a talk may still be influenced by the knowledge that the company rep is the one who is going to be driving you back to the airport.

The practice of doctors passing along free drug samples to patients is also of concern to me and others in the medical community. Seventy-eight percent of the physicians surveyed reported giving free samples to patients who otherwise could not afford to pay for their medication.

The downside of this practice is that if a free sample proves effective, the physician may end up prescribing the drug even if it costs more than another cheaper drug that works just as well. Some academic medical centers have either banned free samples entirely or have severely limited doctors from accepting them. .

These are just a few examples of ways in which physicians, without ever recognizing it, may be subtly or not so subtly influenced to prescribe a drug sold by a company providing lunch, drinks, or free tickets to games and other events (a practice reported by 7 percent of the physicians in the survey).

Back in 2002, the Pharmaceutical Research and Manufacturers of America, with prodding from the American Medical Association, adopted its own set of voluntary rules to limit the value of gifts to physicians and to ban altogether the practice of furnishing free entertainment tickets.

But this latest study shows there's been little change in practices since that time.