12. THE PLACEBO EFFECT Previous | Next

Medicine’s Uncertainty Principle.

I have a feature on placebo in this week’s New Scientist. It’s basically about how studies are showing that every facet of medicine, from primary patient care to clinical trials of pharmaceuticals, is subject to “contextual effects”, where the patient’s state of mind, awareness of their condition, and expectations of care affect the efficacy of treatment. Many of these factors are open to manipulation. So, is our growing understanding of the placebo effect a problem or an opportunity?

For many doctors, it is an opportunity – but it comes at a price. A study published earlier this year showed that nearly half of US physicians deliberately use the placebo effect in their clinical prescribing. However, less than half of these tell the patient what they are doing. Such attitudes are ethically questionable. It is still far from proven that the placebo effect has measurable clinical benefits, so embracing deception in a relationship predicated on trust seems premature. Especially since it might be possible to use the placebo effect without employing deception.

As well as my experience of succumbing to placebo, which I describe in the feature and 13 Things… earlier this year a study showed that children with Attention Deficit Hyperactivity Disorder can manage on reduced stimulant medication if they also take what they are explicitly told is “a ‘dose extender’ or ‘placebo’.” This extra “booster” capsule, the children are told, “has no drug in it… but it may help you to help yourself.” Teachers, parents and doctors reported that cutting the children’s stimulant dose in half, while openly supplementing it with a placebo, made no difference to their symptoms.

It is unclear whether this is more than a short-term effect, but with many drugs having side-effects, such “open-label” use of placebos holds great potential for improving health care. The American Medical Association’s Council on Ethical and Judicial Affairs has recommended that physicians be allowed to use placebos as long as there is this kind of informed consent.

My feature argues that the problem side of the placebo effect will be felt most in examinations of the way we conduct clinical trials of pharmaceuticals. The placebo effect can be triggered by a variety of circumstances with varying effects. Because of all this uncertainty, the standard idea of simply “testing against placebo” is beginning to look inadequate.

However, even here there is opportunity. New drugs have to perform better than placebo in order to be licensed, but placebo rates in clinical trials have been rising. Placebo rates in trials of drugs meant to combat depressive disorders, for example, showed a 20 per cent rise between 1984 and 1997. The source of this “placebo drift” is still largely unknown, but it means the pharmaceutical industry is running to stand still. Any insight that could account for the rising placebo response might help bring effective new drugs to market.

Practitioners of complementary and alternative medicine – such as homeopathy –  probably have the most to lose from our awareness of the complexity of placebo. As the various types and causes of placebo effect are traced, CAM treatments may find themselves with no room for manoeuvre. A performance that is currently better than placebo may disappear once it can be matched by a particular kind of placebo response.

In physics, the uncertainty principle describes where certain combinations of measurements can’t be taken with perfect accuracy – the position and momentum of a particle, for instance. In medicine, we may have found a similar phenomenon in the placebo effect. Physicists have overcome the frustrations of the uncertainty principle and learned to appreciate how it sheds light on their field. I can’t help but think that medicine might find that the placebo effect, once it is properly understood, is similarly useful.