Depression is not caused by a ‘chemical imbalance’ in the brain

A long-held belief is that depression is caused by a chemical imbalance. (Credit: Getty)

There is no clear evidence that depression is caused by low serotonin levels, research suggests.

The new review, which analyzed existing studies, suggests that the condition is not likely caused by a chemical imbalance. and questions what antidepressants do.

Researchers say their findings are important, as studies show that as many as 85-90% of the public believe that depression is caused by low serotonin levels or a chemical imbalance.

Most antidepressants are selective serotonin reuptake inhibitors (SSRIs) and were originally said to work by correcting abnormally low serotonin levels.

There is no other accepted way that antidepressants affect the symptoms of depression.

Lead author Joanna Moncrieff, a professor of psychiatry at UCL, is a consultant psychiatrist with the North East London NHS Foundation Trust (NELFT).

She said: “It’s always difficult to prove a negative, but I think we can safely say that after a huge amount of research over several decades, there is no convincing evidence that depression is caused by serotonin abnormalities, particularly by lower levels or decreased activity of serotonin.

‘The popularity of the ‘chemical imbalance’ theory of depression has coincided with a huge increase in the use of antidepressants.

“Prescriptions for antidepressants have risen dramatically since the 1990s, with one in six adults in England and 2% of teenagers now being prescribed an antidepressant in any given year.”

“The popularity of the ‘chemical imbalance’ theory of depression has coincided with a huge increase in the use of antidepressants.”

“Many people take antidepressants because they have come to believe that their depression has a biochemical cause, but this new research suggests that this belief is not based on evidence.”

Professor Moncrieff added: ‘Thousands of people suffer from side effects of antidepressants, including the severe withdrawal symptoms that can occur when people try to stop them, yet the number of prescription drugs continues to rise.

“We think this situation is partly caused by the false belief that depression is due to a chemical imbalance.

“It is high time to inform the public that this belief is not based on science.”

The overarching review looked at all relevant studies published in the key research areas of serotonin and depression.

In total there were tens of thousands of participants.

Among the findings was that research comparing the levels of serotonin and its breakdown products in the blood or cerebrospinal fluid found no difference between people diagnosed with depression and healthy people.

The authors also looked at studies in which serotonin levels were artificially lowered in hundreds of people.

These studies have been cited to show that a serotonin deficiency is linked to depression.

But a review of the available research in 2007 and a sample of recent studies showed that lowering serotonin in this way did not cause depression in hundreds of healthy volunteers.

Other studies looked at the effects of stressful life events and found that the more stressful life events a person had experienced, the more likely they were to be depressed.

An early study found a link between stressful events, the type of serotonin transporter gene a person had, and the likelihood of depression.

However, larger, more comprehensive studies suggest this was a false finding.

These findings led the authors to conclude that there is “no support for the hypothesis that depression is caused by decreased serotonin activity or concentrations.”

Previous studies have linked depression to serotonin levels (Credits: Getty)

There is some evidence that the belief that a bad mood is caused by a chemical imbalance leads people to have a pessimistic view of the likelihood of recovery and the ability to manage moods without medical help.

According to the study, there is also evidence from other studies that people taking antidepressants had lower levels of serotonin in their blood.

The scientists say this indicates that some evidence was consistent with the possibility that long-term use of antidepressants lowers serotonin levels.

This may mean that the short-term increase in serotonin that some antidepressants produce can lead to compensatory changes in the brain that have the opposite effect in the long term.

Professor Moncrieff said: ‘We don’t understand exactly what antidepressants do to the brain, and by giving people this kind of misinformation, they can’t make an informed decision about whether or not to take antidepressants.’

The researchers caution that anyone considering withdrawal from antidepressants should seek the advice of a health professional.

The findings are published in Molecular Psychiatry.

A spokesperson for the Royal College of Psychiatrists said: ‘Antidepressants will vary in effectiveness for different people, and the reasons for this are complex, so it is important that patient care is based on the needs of each individual and reviewed regularly.

“Continued research into treatments for depression is important to help us better understand how drugs work and how effective they are.

“Medication should be available to everyone who needs it. We do not recommend anyone to stop taking antidepressants based on this review, and encourage anyone concerned about their medication to contact their GP.”

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