Participants in drug trials are often not fully informed about the effect of placebos, thereby undermining the process of “informed consent”, concludes a new study published this week in the open access journal PLoS ONE.

Placebos are used in randomized drug trials to act as a yardstick or constant against which to compare the effect of the drug being tested, the “target”.

Although often thought as “inert” pills, placebos can cause significant health changes, say researchers from the University of Southampton in the UK, and Harvard Medical School and Northern Arizona University, in the US.

Lead investigator, Dr Felicity Bishop, who lectures in psychology at Southampton, told the press:

“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. At the moment these effects are largely being ignored in the participant information leaflets.”

Before taking part in a drug trial, participants give “informed consent” to show they have been given full information about the currently known changes to health that may occur.

But it appears that in some cases, the information falls short where placebos are concerned, said the researchers.

“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,” said Bishop.

For their study, Bishop and colleagues analyzed the content of 45 participant information leaflets from recent high quality clinical trials that used placebos. The trials are listed in the UK Clinical Research Network Database.

They noticed that target treatments were given priority over placebos. This was noticeable from the words used in the titles, through the description of the trial process, to explanations of what happens at the end of the trial. The researchers also observed that:

  • Placebos were referred to significantly less often than target treatments.
  • Placebos were often described in negative terms, using words like “dummy” or “fake”, while target drugs were often described in relation to a class, such as statins (cholesterol lowering) or antibiotics (infection fighting), thus implying they had a particular effect.
  • Placebos were rarely described in their own right: in most cases they were referred to in comparison to the target treatment.
  • On the other hand, target drugs were often described as “genuine”, or “real”, and the focus of the trial.
  • The information emphasized the potential benefits and side effects of the target drug but largely ignored what might result from taking the placebo.
  • The leaflets emphasized the target treatment as being more desirable than the placebo.
  • Eight of the leaflets (18%) explicitly stated that the placebo treatment was either undesirable or ineffective.

Bishop and colleagues conclude that participant information leaflets “provide incomplete and at times inaccurate information about placebos.”

“Trial participants should be more fully informed about the health changes that they might experience from a placebo. To do otherwise jeopardises informed consent and is inconsistent with not only the science of placebos but also the fundamental rationale underpinning placebo controlled trials,” they add.

Professor of Health Research at the University of Southampton, George Lewith, comments on the potential implications of the study:

“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.”

He said from their own studies at Southampton they have seen that placebos can help about half the people they treat for chronic pain, and the effect can last a long time afterwards.

In those trials, the placebo effect works by releasing patients’ own natural painkillers into their nervous system, he added.

If volunteers taking part in clinical trials are not given full information about the health changes that might occur as a result of taking placebos, then their “informed consent”, a crucial part of the trial process, is questionable, argue the researchers.

They recommend that different ways of describing placebos and their potential effects should now be tested, not only where such information appears in leaflets, but also in how it is communicated by researchers and administrators who have personal contact with participants in drug trials.

Southampton University’s Faculty of Medicine funded the study.

Written by Catharine Paddock