Medical professionals such as psychiatrists are more likely to emphasise the biological and biochemical factors involved in depressive illness. Psychologists and sociologists tend to pay more attention to the ways in which people think about the world and to the terrible experiences the world sometimes dishes out to us.

Though almost all mental health professionals would agree that depression involves social, psychological and biochemical factors, the relative importance they place on each has clear implications for treatment. For example, most psychologists will place more emphasis on talking about problems, whereas psychiatrists are more likely to recommend drug treatments.

Depression sufferers seeking help should inform themselves about different approaches to causes and treatment before selecting a mental health helper. An effective therapeutic relationship involves co-operation and trust, and getting the kind of treatment that is right for each individual is important for recovery.

Some mental health problems are more clearly biochemically based (and/or more susceptible to drug treatment) than psychological and vice versa. Bipolar disorder (formerly called manic depression) is not simply a chemical imbalance but, nevertheless, many sufferers control their condition very effectively by taking the drug lithium.

Other depression sufferers become trapped in negative attitudes and thought patterns. For these, cognitive behavioral therapy (CBT) and retraining cognitive habits can be the solution. But CBT is not the recommended treatment for bipolar disorder, just as lithium will be useless for depression that is based on cognitive problems.

Some cases of depression are triggered by painful life experiences. Sometimes supportive talking therapies are needed to help a person through a very bad patch. Though drugs may sometimes take the edge off the pain associated with bereavement, they will not solve the problem and can even become a problem. A combination of supportive therapies and drug treatments are the answer for some people, depending on individual cases.

Often what people suffer from is not depression, but a bad phase that will pass. Even psychiatrists may caution against placing too much emphasis on biology rather than life circumstances. The difference is something all sufferers from depression can appreciate.