Here's an interesting article in the New York Times, describing widespread use of placebos in treating patients, as a way to treat the patient's mental state rather than the actual problem.

The problem is that the placebos used are not inert -- rather, they prescribe drugs intended for other uses, such as headache pills, sedatives, or other relatively harmless drugs.

Half of all American doctors responding to a nationwide survey say they regularly prescribe placebos to patients. The results trouble medical ethicists, who say more research is needed to determine whether doctors must deceive patients in order for placebos to work.

[snip]

The most common placebos the American doctors reported using were headache pills and vitamins, but a significant number also reported prescribing antibiotics and sedatives. Although these drugs, contrary to the usual definition of placebos, are not inert, doctors reported using them for their effect on patients’ psyches, not their bodies.

In most cases, doctors who recommended placebos described them to patients as “a medicine not typically used for your condition but might benefit you,” the survey found. Only 5 percent described the treatment to patients as “a placebo.”

[snip]

Dr. William Schreiber, an internist in Louisville, Ky., at first said in an interview that he did not believe the survey’s results, because, he said, few doctors he knows routinely prescribe placebos.

But when asked how he treated fibromyalgia or other conditions that many doctors suspect are largely psychosomatic, Dr. Schreiber changed his mind. “The problem is that most of those people are very difficult patients, and it’s a whole lot easier to give them something like a big dose of Aleve,” he said. “Is that a placebo treatment? Depending on how you define it, I guess it is.”
Link.

Does your doctor consider you a difficult patient? Would he (or she) tell you if he did? You need to know what your doctor is prescribing -- check the Physicians' Desk Reference (Pdr) or the The Merck Manual, understand the approved uses and known side effects of those drugs.