For a long time our understanding of depression, and what people with the condition are often told, has been that it’s caused by a chemical imbalance in your brain, when it doesn’t produce enough serotonin – the happy chemical.
But a major new research review of dozens of studies into this subject area has concluded that depression isn’t necessarily caused by a lack of serotonin.
What could be more strongly associated with the condition are negative life events that lower your mood, found University College London academics, who looked at existing overviews of research on serotonin and depression for their umbrella review, which has been published in Molecular Psychiatry.
The review could reshape the way we think about the treatment of depression, said the UCL team, although other clinicians have said the idea that depression is down to a simple chemical imbalance is already out of date, while stressing that antidepressants remain a useful option alongside talking therapies.
Among the 7.3 million Brits in the UK on anti-depressants (that’s 17% of the population), the belief that they have a chemical imbalance may actually lead people to have a pessimistic overview of life – believing that it’s out of their control and making them less likely to seek treatment, said the scientists.
“I think we can safely say that after a vast amount of research conducted over several decades, there is no convincing evidence that depression is caused by serotonin abnormalities, particularly by lower levels or reduced activity of serotonin,” said the review’s lead author Joanna Moncrieff, a professor of psychiatry at UCL.
She added: “Many people take antidepressants because they have been led to believe their depression has a biochemical cause, but this research suggests this belief is not grounded in evidence.”
Selective serotonin re-uptake inhibitors (SSRIs) are currently typically prescribed as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions.
But the researchers said that while antidepressants are prescribed to one in six of the UK adult population according to Lancet figures, there isn’t enough evidence to suggest they administer the correct levels of chemicals to the brain.
From their analysis of other studies, the UCL team found that depression levels were not increased in people whose serotonin levels were artificially lowered.
Stressful life events which make people more likely to be depressed were found to a bigger contributor. This is important, say the reviewers, as currently 80-90% of the population think depression is solely down to low serotonin or a chemical imbalance.
Co-author of the UCL review, Dr Mark Horowitz, a training psychiatrist and clinical research fellow in psychiatry said: “I had been taught that depression was caused by low serotonin in my psychiatry training and had even taught this to students in my own lectures. Being involved in this research was eye-opening and feels like everything I thought I knew has been flipped upside down.
“One interesting aspect in the studies we examined was how strong an effect adverse life events played in depression, suggesting low mood is a response to people’s lives and cannot be boiled down to a simple chemical equation.”
The UCL review doesn’t mean we should throw out anti-depressants, the researchers stressed, but that more work is needed to be done to figure out just how they work – as it might not be as simple as increasing serotonin levels.
However, commenting on the research, Allan Young, director of the centre for affective disorders at the Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, told the BMJ that very few psychiatrists subscribe to a simple chemical imbalance theory anyway.
“The use of these drugs is based on clinical trial evidence which informs their use for patients. This review does not change that,” he said.
In a statement, the Royal College of Psychiatrists said: “Antidepressants will vary in effectiveness for different people, and the reasons for this are complex, which is why it’s important that patient care is based on each individual’s needs and reviewed regularly.
“Continued research into treatments for depression is important to help us better understand how medications work as well as their effectiveness. Medication should be available for anyone who needs it.
“We would not recommend for anyone to stop taking their antidepressants based on this review, and encourage anyone with concerns about their medication to contact their GP.”