Many of my friends suffer from depression - as have I, on and off, for the past 12 years. Every morning I take a small dose of antidepressant and I would not give it up without the agreement of my psychiatrist.

The diagnosis for depression is not always clear because there is still no clinical test to establish its presence. Instead, the standard diagnosis reflects the feelings of the patient - suicidal, sleepless, anxious, fatigued and so on. There is a lumpy continuum from feeling low to severe clinical depression.

There are claims that for this reason depression is over-diagnosed. Certainly, the NHS spends hundreds of millions of pounds a year on antidepressants. However, depression affects 20 per cent of the population at some point in their lives.

Now a study of a number of clinical trials has concluded that for most patients SSRI (selective serotonin reuptake inhibitors) antidepressants worked no better than a placebo. It did, however, find that those with a severe depression were helped.

My worry is that this study - and the headlines it has generated - will encourage patients taking antidepressants to give them up. It might also stop those contemplating taking them from doing so. This could have quite serious consequences. I worry we do not know how reliable this new study is.

There is general resistance to taking pills for depression and I sometimes wonder whether antidepressants such as Prozac would be more socially acceptable if they grew on trees.

Of course there are many other ways of treating depression that can be extremely helpful. I am an evangelist for cognitive therapy, which helped me so much. It is quite different, thank goodness, from psychoanalysis, and its main aim is to deal with the all-pervasive negative thoughts that characterise depression.

Exercise can be invaluable too. I favour jogging.

Professor Wolpert is the author of Malignant Sadness: The Anatomy of Depression (Faber and Faber)

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