Research: Depression is probably not caused by a chemical imbalance in the brain

For the past 30 years, people have been told that depression is caused by a chemical imbalance in the brain. The evidence does not support it.

In association with its efforts to market a new range of antidepressants, the pharmaceutical industry began to promote the theory of depression known as the serotonin theory. The American Psychiatric Association told the public that differences in certain chemicals in the brain may contribute to symptoms of depression.

Doctors have repeated the message all over the world. The people were told what to do. A lot of people started taking antidepressants because they thought they had a problem with their brain. One in six of the adult population in England has been prescribed an anti-depressant in the last year.

Some leading psychiatrists have suggested that there is no evidence to support the idea that depression is caused by low or inactive serotonin. The theory continues to be endorsed by others. There hasn't been a comprehensive review of the research on the effects of depression or Serotonin.

The theory of depression is supported by the fact that the antidepressants act on the Serotonin system. This does not mean that depression is caused by the opposite of the effect of the SSRIs.

There are other explanations for drugs. Drug trials show that the difference between a placebo and an antidepressants is small. Although we don't know how this effect is produced or much about it, antidepressants seem to have a generalized emotion-numbing effect which may influence people's moods.

First comprehensive review

Since the 1990s there has been a lot of research on the serotonin system. In order to conduct anumbrella review, we systematically identified and gathered the evidence from each of the main areas of research. There have been systematic reviews of individual areas in the past, but no evidence from all the different areas taking this approach

Serotonin levels in the blood and brain fluid were compared in a research project. The research did not show a difference between the two groups.

Serotoninreceptors, which are the end of the nerves that link up with Serotonin, are the focus of another area of research. There was no difference between people with depression and people without depression, and there was no difference between people with depression and people without depression, according to research.

There is research that suggests that people with depression have increased activity in the Serotonin Transporter. The findings may be explained by the fact that many of the people in the studies were using antidepressants.

There is research that explored whether depression can be caused by artificially lowering the levels of a brain chemical. There were two systematic reviews from 2006 and 2007, and a sample of the ten most recent studies that found no evidence of depression in hundreds of volunteers. There was only a small subgroup of people with a family history of depression who were shown to have an effect in one of the reviews.

Large studies involving tens of thousands of patients looked at the variation of the genes. They didn't find a difference in the frequencies of the genes between people with and without depression.

A famous early study found a relationship between the serotonin transporter gene and stress, but larger, more comprehensive studies suggest that is not the case. People with stress in their lives are more likely to develop depression.

Some of the studies that included people who were taking or had previously taken antidepressants showed that they may have a negative effect on the activity of the brain chemical Serotonin.

Not supported by the evidence

One of the most influential and extensively researched theories of the origins of depression is the Serotonin Theory. Scientific evidence does not support this view. The basis for the use of antidepressants is questioned.

Serotonin is believed to act via the antidepressants' effects. The brain chemical noradrenaline is affected by some. The evidence for noradrenaline's involvement in depression is not as strong as that for Serotonin.

There is no other accepted way to treat depression. It's not clear if antidepressants do more good than harm if they exert their effects as placebos.

Research shows that people who believe their own depression is due to a chemical imbalance are more pessimistic about their chances of recovery.

People should know that the idea that depression is caused by a chemical imbalance is not real. We don't know what happens to the brain when there are temporarily elevated levels of Serotonin in the system. It is not possible to say that taking SSRI antidepressants is worth it.

It is very important that you speak to your doctor first if you are on antidepressants. People need this information to make informed decisions about whether or not to use these drugs.

Mark Horowitz is a clinical research fellow in Psychiatry at the University College London.

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