And many doctors fail to make it clear these treatments don't really do anything for the specific ailment for which they are prescribed, the survey found. That contradicts advice from the American Medical Association, which recommends doctors only use treatments with the full knowledge of their patients.
"It's a disturbing finding," said Franklin G. Miller, director of the research ethics program at the US National Institutes of Health and one of the study authors. "There is an element of deception here which is contrary to the principle of informed consent."
The study was being published online in Friday's edition of BMJ, formerly the British Medical Journal. Placebos as defined in the survey went beyond the typical sugar pill commonly used in medical studies. A placebo was any treatment that wouldn't necessarily help the patient.
Studies have shown that patients given a fake or ineffective treatment can often improve, despite the pill having no known effect on their condition. "It seems like doctors are doing things they shouldn't be doing," said Irving Kirsch, a professor of psychology at the University of Hull in Britain, who has studied the use of placebos.
How the study was done
"Doctors may be under a lot of pressure to help their patients, but this is not an acceptable shortcut," he said. Researchers at the NIH sent surveys to a random sample of 1 200 internists and rheumatologists - doctors who treat arthritis and other joint problems.
They received 679 responses, of which 62% believed that using placebo treatment was ethically acceptable. Half of the doctors reported using placebos several times a month.
Nearly 70% of those who did so described the treatment to their patients as "a potentially beneficial medicine not typically used for your condition." Only 5% of doctors explicitly called it a placebo treatment.
Most doctors used actual medicines as a placebo treatment: 41% used painkillers, 38% used vitamins, 13% used antibiotics, 13% used sedatives, 3% used saline injections and 2% used sugar pills.
In the survey, doctors were asked if they would recommend a sugar pill for patients with chronic pain if it had been shown to be more effective than no treatment. Nearly 60% said they would. Smaller studies done elsewhere, including Britain, Denmark and Sweden, have found similar results.
'Doing something better than doing nothing'
Jon Tilburt, the lead author of the US study, who is with NIH's bioethics department, said he believes the doctors surveyed were representative of internists and rheumatologists across the US.
No statistical work was done to establish whether the survey results would apply to other medical specialists like paediatricians or surgeons. The research was paid for by the NIH bioethics department and the National Centre for Complementary and Alternative Medicine.
The authors said that most doctors probably reasoned that doing something was better than doing nothing. Situations where placebos were used included conditions such as chronic fatigue syndrome, or giving antibiotics to patients with viral bronchitis, knowing that a virus isn't susceptible to antibiotics.
Scientists still don't understand how the placebo effect works - whether it is just psychological or whether there is also a physiological reaction. Some doctors believe placebos are a good treatment in certain situations, as long as patients are told what they are being given.
Possible to get psychological impact without pills
Dr Walter Brown, a professor of psychiatry at Brown and Tufts Universities, said that people with insomnia, depression or high blood pressure often respond well to placebo treatments.
"You could tell those patients that this is something that doesn't have any medicine in it, but has been shown to work in people with your condition," he suggested. Brown said that while he hasn't prescribed sugar pills, he has given people with anxiety problems pills that had extremely low doses of medication. "The dose was so low that whatever effect the patients were getting was probably a placebo effect," he said.
Kirsch, the psychologist, said it might be possible to get the psychological impact without using a fake pill. "If doctors just spent more time with their patients so they felt more reassured, that might help," he said.
Experts also don't know if the placebo effect would be undermined if patients were explicitly told they were getting a dummy pill. But some patients who had just seen their doctors at a clinic in London said the truth was paramount.
"I would feel very cheated if I was given a placebo," said Ruth Schachter, an 86-year-old Londoner with skin cancer. "I like to have my eyes wide open, even if it's bad news," she said. "If I'm given something without being warned what it is, I certainly would not trust the doctor again." – (Sapa, October 2008)