The Times receives many letters and questions about depression. Below is a compilation of Dr Thomas Stuttaford’s Q&As on the subject covering all aspects of the illness beginning with basic information and moving on to advice on specific symptoms, medications and treatments.

(Dr Stuttaford’s replies cannot apply to individual cases and should be taken in a general context. Please consult your GP if you suffer from any health or special conditions.)

Can depression be cured or should one just sit it out? Eric Wilding, Devon

Depression is not a single disease with a single cause. It is a syndrome of symptoms that have widely differing causes. The patient with the classic depressive symptoms - the early morning waking, the diurnal variation, the loss of weight, the feelings of hopelessness, the loss of appetite both for food and sex, a lack of enthusiasm for work and interest in social activities, usually responds well and quickly to medication but this needs to be continued for at least six months and to be tailed off slowly. Evidence shows that the best treatment for these cases is a combination of medication and cognitive behavioural therapy.

Is depression more likely at certain important periods of life, such as adolescence and retirement? Name and address withheld

Yes. Adolescence is an appallingly stressful time. The problem with depression in adolescence is to sort out those adolescents who are only reacting badly, but not in an uncommon way, to the problems adolescence brings from those in whom the depressive state is the first sign of bipolar disease, schizophreniform behaviour or true clinical depression. Any young person who suffers from depressive troubles is exceptionally foolhardy to take cannabis.

Retirement involves not only a change in lifestyle but also in self assessment. The retired cease to be able to understand their immediate use to the community and for those who have been brought up with the work ethos this can be devastating. Their status in the community, the family and in their own minds takes a beating once they haven't a working role. They may also have to re-orientate their approach to their husbands or wives. If the wife has been at home all day the regular and constant presence of a husband may be depressing, and however much a husband may have liked his wife he may not want to spend 24 hours a day with her.

How do you know when is the right time to come off anti-depressants if you have more reactive depression to a certain situation of incredibly stressful job, which has now been resolved and you are feeling happier and don't want to rely on the tablets to balance your emotions?m Name and address withheld

This question raises the point that anti-depressants must never be left off suddenly. So long as the anti-depressant have been taken for at least six months and the patient has now cheered up, especially if they have not only cheered up but the anxiety that was a factor in inducing the depressed state has been removed, the anti-depressant may then be tailed off. This must always be done after taking the advice of the GP. Anti-depressant treatment should never be abandoned even if it doesn't seem to be helping without the full knowledge of the doctor. Patients have to realise that for some cases long term anti-depressants are necessary, and if the depression recurs they may have to go back onto them.

Why is it so difficult to find out the cause of depression, surely with today's MRI scanners this must make it an easy task? Mike McKeary, Paisley

Even functional MRI scans essentially illustrate which part of the brain is activated by certain activities. They don't, and at the moment can't, give us any idea of the biochemical changes that are accompanying this action. Depression is the result of changes within the biochemistry of the brain rather than its structure.

Is there any evidence that prescription antidepressants work better than St John's wort? Also, has any research been done into the use of food colourings to "kick start" somebody suffering depression? Colours such as tartrazine and sunset yellow that cause hyperactivity in children seem to work well in overcoming the lethargy associated with depression. Jeremy Bushell, Exeter