I have a confession to make. I throw my hands up, safe in the knowledge that a great many doctors have performed the same misdeed. I like to think that my prescribing habits are sensible. I read and appraise the latest research, ensure I am aware of Government advice and, whenever possible, practise evidence-based medicine. Despite this, there have been times when I have prescribed medication knowing that it isn't going to work.

The symptoms are some of the most disheartening that doctors have to face: a sigh and a roll of the eyes. Sometimes, these develop into a raised voice or even foul language. And the medication guaranteed to abate them? Antibiotics.

Most ailments such as colds, sore throats and chest infections are caused by viruses for which there is no medical treatment. Most people know this, yet they ask for drugs anyway. When refused, they get upset. On the occasions that I have relented, I've been amazed by the transformation: they smile and say thank you.

It has happened to me on psychiatric wards, but is more of a dilemma in general practice. Figures show that a quarter of people visit their GP every year because of coughs and colds, and these account for 60 per cent of all antibiotic prescriptions in general practice. Surely doctors should know better? But the situation has got so out of hand that last week the National Institute for Health and Clinical Evidence (NICE) issued guidelines reminding GPs not to prescribe antibiotics for conditions caused by viruses. This exposes how medication operates on a symbolic level for both doctors and patients.

There are times when we all like to believe that medicine can provide a magic bullet. The idea that there must be a drug for every disease was proposed by the Renaissance physician and alchemist, Paracelsus. Despite now knowing this is not the case, the idea endures today as an artefact of our faith in medicine. Doctors collude with this mythology because it gives them the illusion of omnipotence and control.

People expect to leave their doctor with something tangible. That a prescription might not be clinically indicated isn't important. Its benefits operate on a psycho-social level, validating their illness. They do not want to be told to go home, watch TV and wait to get better. Doctors can risk a patient's wrath by telling them they should let their immune system fight it off, or they can prescribe medication.

The latter is a relatively selfish act on behalf of the doctor - it makes his or her life easier in the short term. In the new, consumer-led NHS, it's easier to give patients what they want. In the long term though, it creates heartache for everyone.

Not only do antibiotics cost the NHS £175 million a year but the over-prescribing of them is directly linked to the prevalence of antibiotic-resistant infections such as the superbug MRSA. New strains of superbugs are developing and the situation will get worse if doctors don't rethink their prescribing habits. Telling your patient that nothing can be done for a harmless viral infection may be difficult, but the prospect of telling them that nothing can be done for a life-threatening bacterial one is worse.