What causes depression?

Depression is very common, affecting about one in every 20 people at some point in their lives. It is thought to be caused by inadequate activity of neurons that release serotonin or noradrenaline, which results from a combination of inherited and environmental factors. Short daylight hours in winter trigger one type of depression - seasonal affective disorder (SAD), while postnatal depression can affect mothers during the first year after giving birth.

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Some people get depressed in winter.

Is depression inherited?

Certain people are probably more at risk because of their genes: if one identical twin suffers from depression there is a 60% chance that the other will, too. Since identical twins share identical genes, this shows that while genes have an important influence in depression, other non-genetic (environmental) factors are involved too. About 20% of people have what scientists call the 'short' version of a gene called 5-HTT, and it is these people who are more likely to develop depression after a stressful life event.

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If one identical twin suffers from depression there is a 60 per cent chance that the other will, too.

Can we treat depression?

The first antidepressant was discovered by accident in the 1950s. A drug being used to treat tuberculosis patients (iproniazid) seemed to cheer them up. This drug and other related antidepressants all increase and prolong the actions of serotonin and/or noradrenaline in the brain. The best known of these is Prozac, which exaggerates the actions of serotonin. Helping people to overcome their negative thoughts (cognitive therapy) is also an effective way of treating depression.

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How Prozac works.

What is bipolar disorder?

Bipolar disorder affects around 1 person in 100 at some point in their life. It causes a pattern of extreme mood swings that alternate between depression and mania – when the person feels ‘high’. Bipolar disorder is probably caused by a combination of inherited and environmental factors. The illness can be treated very successfully with lithium, which acts as a mood stabiliser. Alternative treatments are drugs normally used to treat schizophrenia. Little is known about the problems in the brain that cause mania.

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Spike Milligan suffered from manic depression.


Principal Funder:

Wellcome trust

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