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.

The study involved 679 internists and rheumatologists chosen randomly from a national list of such doctors. In response to three questions included as part of the larger survey, about half reported recommending placebos regularly. Surveys in Denmark, Israel, Britain, Sweden and New Zealand have found similar results.

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.”