Illustration: Mick Connolly.
Even those who are not sick can benefit from medication.
IF YOU believe the figures, there's a worldwide epidemic of mental illness. Depression is the fourth biggest cause of disability and disease globally, and it will be the leading cause in developed countries by 2020. You have about a 15 per cent chance of suffering each of anxiety and depression.
Worse, this epidemic is spreading to our children. Last week, The Sunday Age reported that doctors in Australia would soon be screening three-year-olds, under the Healthy Kids Check, for early signs of mental illness, including anxiety. They aim to tackle behaviours like aggression, impulse control and trouble interacting with other children.
This apparent surge in mental illness raises the question: are we unfit for the compressed, high-paced, alienating, competitive world we've created? Maybe. But let's ask a different, more challenging question. When is it justifiable to prescribe medication - only when there is a diagnosed deficit or disease; or should we use it to enhance our lives as much as possible?
The meteoric rise in mental illness is due, in part, to three factors: increased willingness to diagnose mental illness, a relaxation of diagnostic criteria and the invention of new mental diseases, some of which I would argue are simply part of normal, human variation.
The ''bible'' of mental illness is the Diagnostic and Statistical Manual of Mental Disorders, a fifth edition of which is imminent. The initial draft included the new ''mental'' disorders of shyness, substance use (making it the same as dependence), and eccentric behaviour. Changes in the definition of alcoholism would have meant 40 per cent of American college students were classified alcoholics. Even grieving for a relative could be a disorder: ''persistent complex bereavement-related disorder''.
The eagerness to label mental illness doesn't stop there. Especially tantalising is the new ADHD diagnosis - ''attention deficit/hyperactivity disorder (ADHD) not elsewhere classified'' - which is for people who don't in fact meet the criteria for a diagnosis of ADHD.
Severe PMT is now an official mood disorder: ''premenstrual dysphoric disorder''. Temper tantrums may be ''disruptive mood dysregulation disorder in children''. And the American Psychiatric Association has even considered the idea of ''internet addiction''.
Have the psychiatrists gone mad? Are they pathologising the normal?
Doctors are redefining normal variation as a disease. Professor Allen Frances, who chaired the last DSM edition, even admitted that childhood epidemics of autism, bipolar disorder and attention deficit disorder had led to widespread mislabelling and overmedicating - partly in order to enable insurance coverage in the US.
But it is more complicated than that. Doctors and society draw a clear line between treatment of disease and the enhancement (or improvement) of normal people, or making people ''better than well''.
But that line is a statistical one - the bottom 2 per cent of the population for any characteristic, as is done with IQ, are said to have a ''disease'' and offered treatment. But often the bottom 30 per cent, or even 50 per cent, will still significantly benefit from enhancement.
Part of the reason for the explosion of mental illness is that you can't get effective drugs unless you are suffering from a disease. Society steadfastly refuses to medicate or enhance normal people. So, if you want to make them better by giving them a drug, you call them diseased or disordered.
The fact is that a substantial proportion of mental health promotion and psychiatry is the quite legitimate enhancement of normal, human variation.
One of the targets of the Healthy Kids Check is identifying poor impulse control. More than 40 years of research has shown that three-year-old children who are unable to delay gratification, exercise self-control or who have poor impulse control face big obstacles for the rest of their lives. They are more likely to end up in jail and at the bottom of the socio-economic scale. They will have fewer friends and less motivation to succeed. If you can improve impulse control, you will make that child's life better - so why not do it?
The trouble is that poor impulse control is not a disease. It's at the end of a normal spectrum. But doctors' hands are tied. To try to improve this, you have to call it a disease. Because enhancement is a big medical no-no (except in cosmetic surgery).
Redefining normality as disease can lead to abuse. People can be ''treated'' for social reasons. Homosexuality was defined as disease by the American Psychiatric Association until 1973. It was even retained by the DSM until 1986 as ''ego-dystonic homosexuality''. Homosexuals were subjected to the painful aversion therapy depicted in Stanley Kubrick's A Clockwork Orange, in the 1950s and '60s to ''cure'' them.
This was wrong because, among other reasons, homosexuality is not associated with any reduction in wellbeing. The only harm that occurs stems from the prejudiced attitudes of homophobes.
Although it may initially seem disturbing, the Healthy Kids Check aims at legitimate and admirable goals, and is to be applauded. Early intervention is key to preventing problems later in life.
But the question of whether we should treat normal people for their own good or for the protection of others (for example, in the case of psychopathy) is an open question. The answer will turn on how accurate our predictors of behaviour are, how bad these behaviours are, how effective the treatments are, and the costs of such treatment. But most importantly, it turns on ethics - the importance of wellbeing, and of freedom and autonomy.
We can have our cake and eat it too. We could halve the rate of mental illness tomorrow by redefinition. And we could continue to enhance the lives of normal people with the drugs developed in psychiatry.
Julian Savulescu is professor of practical ethics at Oxford University and a distinguished visiting professor at Monash University.