Dr Nick Walsh, lecturer in psychology at the University of East Anglia on the importance of the social environment for antidepressant action

Recent data shows that 70 million people were prescribed antidepressants last year and that this number has doubled in the last 10 years. Prescription rates are also higher in parts of the country exposed to greater social deprivation. This has clearly moved beyond being simply a personal issue and is now also a pressing social issue given the numbers and geographical variation. GPs and journalists are now using the term 'rotten life syndrome' to describe this phenomena.

The best available evidence shows antidepressants are generally effective for adults over an eight-week trial but are not effective for children or adolescents. There is also evidence that for people who take them over much longer periods e.g. 30 years, are worse off compared to comparison groups. There are also many unpleasant side effects and some experience difficulties with withdrawal that need to be carefully managed with clinical care. There are also proposals that they may do more harm than good over the longer term as they prevent the body's normal adaptive stress-coping processes from kicking in to deal with the stress. Strictly speaking, the term 'antidepressant' is incorrect as they are also prescribed for a wide variety of other psychiatric and non-psychiatric conditions.

It is vital people are given an appropriate explanation when being prescribed antidepressants. Online guides such as NHS direct state we don't know exactly how they work. This explanation isn't good enough and research is rapidly improving our understanding, especially about how these drugs affect us psychologically. We know that these drugs affect a person's neurotransmitter levels, and particularly a neurotransmitter called serotonin. However, we know they are not simply 'happy pills' and there is absolutely no scientific evidence that antidepressants correct some kind of 'chemical imbalance' people may have or been born with. This chemical imbalance myth appears to have been created by drug company marketing departments.

The best theory at the moment is that rather than affecting people's mood directly, antidepressants work indirectly to take the brain back to a more juvenile state, and essentially make the brain more plastic. This change in brain plasticity is then thought to enable people to re-learn and modify how they see the world and ideally relearn unhelpful patterns of behaviour.

Even though these drugs take about four weeks to affect people's depressed mood, we know that these drugs affect people psychologically after even a few hours. This can be seen in changes in how people process information, such as detecting emotional expressions in faces. The current thinking suggests that by changing how people process emotional information, they can have less of a bias towards negative information and a changed focus toward more positive information. This greater perceptual flexibility may then change the types of social interactions people have and increase the chances of more rewarding social experiences. This is why having supportive psychotherapy in conjunction with antidepressant treatment works better than antidepressant treatment alone.

However, because antidepressant treatment can affect our sensitivity to our environment, this can be both a good or bad thing depending on what kind of social environment we're in. Other research shows that higher doses of antidepressants can amplify the likelihood of positive outcome in supportive environments. But this research also shows that greater plasticity through increasing antidepressant doses may also make us more susceptible to the negative effects of stressful environments.

Consideration of social environment is therefore critical as the patient's social environment may interact with the medication. This could be an explanation for why antidepressants are less effective in groups exposed to more stress, e.g. young people and those living and working in deprived parts of the country. The take-home message from this is it is not enough to tell people to go away, take their pills and the problem will be fixed. Clinical practice now needs to recognise that the problem is not simply in the person, the problem lies in a person's relationship with their social environment.