Among the many big questions that vex GPs on a daily basis ("Who's turn is it to visit the nursing home?" "What shall we do with the bearded receptionist?" "How did the hamster get up there, anyway?"), the biggest is: "Why can't we bring back the Smartie?" Now to you, Smarties may never have gone away, but you won't get any on prescription these days, which is a great pity because they're the safest and most powerful therapy known to man. We used to be able to dish out Smarties by the bucketful along with Pillula Panis (bread pills), Aq Menth. Pip. (peppermint water) and the Pink Medicine (ingredients unknown). All were cheap, harmless and yet gave enormous benefit to countless patients every day. So why have they been banned?

Before we tackle this riveting ethical conundrum, let us ponder the placebo effect. How can a pill with no active drug in it whatsoever give a patient enormous benefit? Debating this single question could easily have occupied the whole of National Science Week, but suffice to say that the human mind is very susceptible to suggestion and expectation. The effects can be pleasing (hence placebo - "I will please") or humiliating (a stage hypnotist turning you into a chicken on acid). Placebos have been used by faith healers, aromatherapists and druids since the Flintstone era, but the first documented use by a British doctor was in 1890, when a woman was given painkilling injections of water, believing them to be morphine. The jabs worked a treat, but when she discovered the deception, she got rather shirty and called in the lawyers. Plus ca change.

More recently (1986, in fact), patients with swollen cheeks after wisdom tooth extraction received ultrasound therapy to reduce the swelling. Their jaws shrank by 35 per cent compared with a control group, which was all the more remarkable as the probe wasn't even plugged in. Not everyone was affected equally, and placebos do seem to have better success rates with churchgoers and those who pay for treatment, suggesting an element of emperor's new clothes. It has been unfairly proposed that the strength of the placebo response varies inversely with the combined intelligence of practitioner and patient. I say unfairly because some of the most striking placebo experiments have been done by doctors on medical students. In one study, 56 students were given either a pink or blue sugar pill and told it could be a stimulant, sedative or placebo. Only three said the pills had no effect - 72 per cent of those taking a blue Smartie felt drowsy, 32 per cent on pink Smarties felt less tired and 33 per cent of the whole group reported side-effects such as dizziness, watering eyes and headaches. Bizarre or what?

Richard Asher, a distinguished London wit and physician, was spot on when he observed: "Success of therapy depends as much on the enthusiasm of the therapist as the faith of the patient. If you fervently believe in your treatment, even if controlled trials show it is quite useless, your results are much better, your patients are much better and your income is much better, too." But what, for a patient, does "better" mean? Doctors generally try to draw a distinction between feeling better and getting better. Placebos make you feel better, but they don't make you get better, in the sense that they don't cause changes in your body's tissues we can observe under a microscope. Only a doctor can do this for you.

I certainly swallowed this as a medical student and scoffed dutifully at populist health books such as The Healing Power of the Mind. But if the mind doesn't have a capacity to heal, what's the point in having one? The proof, as ever, comes from Smarties. They can speed the healing of up to 70 per cent of duodenal ulcers, which should be enough tissue changes to satisfy the greatest sceptic. Unfortunately, this won't satisfy the ethicists who object to the use of placebos on the grounds of deception. These days, we have to tell the truth. We can't say: "Take this tablet of ziprofloxamixotide, the newest and most powerful wonder drug on the market", regardless of how many ulcers it might heal, if we know in reality it's a chocolate button from Bournville.

The death of the placebo has meant the birth of the side-effect. Because deceiving patients with harmless sugar tablets is off-limits, we end up poisoning them with antibiotics, painkillers and tranquillisers when a button would do. The theory now is that doctors should use their bedside manner, not their tablets, as placebos - a bit of reassurance here, a shoulder to cry on there. But when you're on the back end of a weekend shift with six minutes for each patient, manners go out the window and you yearn for a quick fix of the Pink Medicine, which is why I was delighted to hear of the rising of the ethical placebo.

Studies have shown that placebos still work if you tell patients the truth. You can say: "I feel a so-called sugar pill will help you as it has helped many others. A sugar pill is a pill with no medicine in it at all. Are you willing to try this pill?" Unbelievable as it sounds, the ethical placebo has been shown to be effective in relieving pain and raising mood across a wide range of humanity, from neurotics to medics. Patients can be taught to associate Smartie with symptom-free, just as Pavlov's dogs slobbered when the bell rang. However, it works one thing is certain: you should never underestimate the power of the Smartie.