Placebo for Dummies

Placebo, schmebo. I don’t dispute its existence but I just read Counterknowledge and even they seem to fall into what looks like a placebo myth trap. While discussing quackery Damian Thompson makes this comment:

On the other hand, they [alternative therapies] may well match a placebo in effectiveness; and the placebo effect, as any GP will tell you, can be freakishly powerful. About 30 per cent of patients in clinical trials feel better after taking placebos in the form of dummy pills or saline injections.

Well, I’m a GP and I agree. If there is a powerful effect with placebo it is a freak event; it is certainly not the usual outcome.

Bandolier’s Little Book of Making Sense of the Medical Evidence looked at some of the trials that suggest placebo effect. They showed placebo effect ranging from 18-88%. But when aggregated (12,000 patients) the proportion of patients achieving 50% pain relief with placebo in post-op pain was 18%. They say:

Statements suggesting that one-third of people respond to placebo or that people respond to the placebo at one-third of the maximum response are wrong. The information above shows that both are wrong. It takes a long time to debunk widely held beliefs.

Exactly the same criticism that is so often levelled at shoddy CAM trials has been used to build up the placebo myth. I’ll bypass the irony of Counterknowledge perpetuating this myth because it is still an inspired book. The fact is that the large placebo responses in some smaller trials can be explained by chance alone.

This makes much more sense and I think we need to be a darn sight more sceptical about placebos. The problem with over-egging placebo is that it’s one of the issues at the heart of the problem when persuading people that some of the more outlandish alternative therapies are ludicrous. Many people, and in particular GP shruggies, are quite prepared to accept CAM because of the widely perceived wonderfulness of placebo.

Ben Goldacre’s recent Radio 4 programme on placebo (part 2 available here) states that it is:

One of the most effective and neglected evidence based treatments known to man.

This makes for good spin and the programme itself explores lots of the side issues. So Cochrane is fairly well accepted to know their way around the evidence. What do they say?

Placebo interventions for all clinical conditions (Review)

It has been widely believed that placebo (dummy) treatments (for example sugar tablets) are associated with substantial effects on a wide range of health problems. However, this belief is not based on evidence from randomised trials that use a placebo treatment for one group of people, while another group receives no treatment. The effect of placebo treatments was studied by reviewing more than 150 such trials covering many types of health care problems. Placebo treatments caused no major health benefits, although they possibly had a small effect on outcomes reported by patients, for example pain.

They also added:

There was no evidence that placebo interventions in general have clinically important effects. A possible small effect on continuous patient-reported outcomes, especially pain, could not be clearly distinguished from bias.

I am not convinced by that summary that we are neglecting a major therapeutic option.

Are you sure you are doing nothing?

There are difficulties in teasing out what people mean by placebo effect. A clinical trial involves even more dramatic flourishes and theatre than most daily clinical contacts. Trials involve explanations, consent forms and a much greater fanfare than might be expected in a routine surgery appointment. This in itself is an intervention and a side-effect of clinical trials is to ramp up the effect for groups receiving dummy treatments.

I would argue that doctors that have a positive attitude do not ‘amplify’ the placebo effect. It is an obvious intervention and not some latent property of the pill. A fundamental point that homeopathists seems to be struggling to grasp.

Placebo seems to have an almost mythic status as a health intervention. The danger is that it is interpreted as some kind of magical effect; one that is beyond science and rational thought. It feeds an irrational pseudo-science set of beliefs that bubbles below the surface and of which CAM is the overt expression.

Placebo only works with the scaffold of expectation build by practitioners and the system in which it is delivered. We can possibly learn a lot about we how deliver care by studying placebo but we need to temper this with a dose of reality.