Placebo is Latin for "I will please". In medicine it has come to mean a treatment - a sugar pill or saline injection - that, in itself, has no physical effect. In spite of this, placebos have often been found to relieve physical symptoms such as pain, swelling, inflammation, or even depression. Apparently, in such cases, it is the act of treatment rather than the treatment itself that is effective.
At once we are in deep philosophical waters. If pills or injections do nothing, then what is doing something? If, merely by being treated, the patient improves, then the remedy must be in his mind. Thinking makes him better; the mind has power over his body and, therefore, over the physical world. The mind is what it appears to be - an immaterial force. A sci-fi landscape of telepathy, telekinesis and mind-melds suddenly opens before us.
But no. The mind-body problem has, for Dylan Evans, been solved. "The mystery turns out to be an artefact of our confused ways of speaking, such as our tendency to persist in talking about 'mind over matter', as if the mind were not itself a material process. If there is any problem at all, it is that of understanding how one part of the body - the brain - communicates with the rest."
Following Daniel Dennett, Evans says the mind is just what the brain does. I've never understood how this explains anything of significance. Perhaps there is nothing to explain, which is very strange indeed. But what matters for the purposes of this book is that this view of the mind must mean that there can be no ultimate mystery about the placebo effect. It must work through the same biochemical pathways as any other mechanism.
Some mental process, therefore, must have physical effects. This is not surprising in itself - if I am frightened, for example, my heart beats faster - but it is odd in the context of what science has so far understood about the disease symptoms that placebos seem to affect. But Evans has a theory, based on a formidable know-ledge of the vast amount of research in this area.
His starting point is that placebos are not as effective as has often been claimed. In fact, they seem to work in very speci- fic areas associated with "the acute phase response" - symptoms such as pain, swelling and inflammation. They do not cure cancer, nor any other chronic condition. They work through what Evans calls "the belief effect". If patients believe in their treatment, then placebos can be at least as effective as the steroids or analgesics whose physical effects we more or less understand. There are problems for this theory - notably placebos' effect on depression - but Evans shows that there is some evidence that such conditions are physiologically linked to the acute phase response.
Therapies such as psychoanalysis and acupuncture are badly damaged by this idea. Indeed, Evans thinks the evidence shows that they both work through the placebo effect. This may not subvert those disciplines completely (if they work at all, what's the problem?) but it does destroy their theoretical foundations. If patient belief is all that is required, then Oedipal myths and the flow of energy through the meridians are purely cosmetic, the necessary stage dressing for a performance that is entirely fictional.
If everybody reads and accepts this book, then placebos are finished. The belief effect will no longer apply. But if we wish to retain placebos as an effective treatment, we must sustain the illusion, an idea that conflicts with the medical ethical concept of informed consent. Precisely what we cannot do, if placebos are to work, is fully inform the patient. In fact, this issue can be effectively blurred. Evans quotes some hilarious explanations by doctors to patients that managed to be both ethical and effective as far as the placebo was concerned. Patients were told they were being given a sugar pill but in a perverse reinforcement and reversal of the belief effect, they didn't believe the doctors, and the placebo worked.
Why there should be such a thing as the placebo effect remains problematic. Evans speculates, as others have done, that it was selected by evolution as a means of managing the resources of the immune system. Given that placebos seem to work, in part, by suppressing the immune response, they may be a way of conserving the body's energy at critical moments. We may even get depressed to stop us being too active, and so slowing recovery. It is a high price to pay, but then evolution is not a merciful master.
But knowledge of the placebo effect may be more important than we yet realise. Though Evans is generally dismissive of most alternative medicine, he does accept that the way alternative practitioners treat their patients, and thus enhance the placebo effect, may offer an important lesson to conventional medicine.
"Doctors," he writes, "might then discover how to regain the magic they have lost, and research into the placebo response could allow medicine to heal itself."
Evans is a clear and effective, though slightly arid, writer. If he really wants to break into the popular science market, he needs to loosen up a little. And occasionally, he cheats - his argument with Bertrand Russell about the nature of belief is, as I suspect he knows, inadequate. But if you want to know exactly how science intends to invade the human realm, then this is a very good place to start.
Bryan Appleyard's Understanding the Present is to be reissued by I B Tauris