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Patients in the dark on placebo side effects

U. SOUTHAMPTON (UK) — Participants in drug trials should be better informed about the potentially significant benefits and possible side effects of placebos, new research shows.

Placebos, traditionally thought of as inert pills, are given in trials to act as a yardstick or constant by which to measure the effects of new active drugs, known in clinical trials as the target treatment. But placebos themselves have been shown to create substantial health changes in patients.

“We believe the health changes associated with placebos should be better represented in the literature given to patients before they take part in a clinical trial, says Felicity Bishop, a lead researcher at Southampton University and lecturer in psychology.


“At the moment these effects are largely being ignored in the patient information leaflets. There is an important issue of consent here—patients should be fully aware of possible health changes from all treatments in a trial before agreeing to take part.”

For the study, published in the journal PLoS One, researchers examined the wording of 45 participant information leaflets from clinical trials which used placebos and are listed on the UK Clinical Research Network Database. Analysis of the participant leaflets led to these key observations:

  • Emphasis was given to the target treatment being more desirable to receive than the placebo.
  • Target treatments were widely described as “real,” “genuine” and the focus of the study. Placebos were rarely described in their own right, rather they were mostly referred to in comparison to target treatments.
  • Target treatments were often described in relation to a class of drug, thus implying a particular effect, for example, antibiotics (infection fighting) or statins (cholesterol lowering).
  • Placebos were often described in negative terms, such as “dummy” or “fake.”
  • The leaflets emphasized both the benefits and adverse effects that might be triggered by the target treatment, but largely ignored any potential effects of the placebo.

Crucially, the study shows the target treatments were prioritized over the placebo, from the words in the leaflet titles, to the description of the trial process, through to explaining what would happen at the end of the trial.

“The leaflets largely ignored the overwhelming evidence that placebos can actually have significant and sustained effects on people. This could affect the treatment beliefs and expectations of those volunteering for studies and in turn the results,” says George Lewith , professor of health research.

“Studies at Southampton have clearly shown placebos can help about half of the people we treat with chronic pain and can be effective for a long time afterwards. The placebo effect works by releasing our bodies’ own natural painkillers into our nervous system.”

The researchers argue that volunteers for clinical trials should be more fully informed about the health changes they might experience from a placebo, otherwise their informed consent, crucial to taking part, is in jeopardy. Different ways of describing placebos need to be developed and tested, both for participant information leaflets and for personal contact with those conducting research, they say.

Researchers from Harvard Medical School and Northern Arizona University contributed to the study that was funded by Primary Care and Population Science, part of the Faculty of Medicine, at the University of Southampton.

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