“The main areas of serotonin research provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations.” *
Depression: A Serotonin Deficiency?
For decades now people have been led to believe that depression is caused by a chemical imbalance in the brain due to a deficiency of the brain chemical serotonin. Yesterday, [July 20,2022] the prestigious journal Molecular Psychiatry published the first exhaustive review of the main research on links between depression and serotonin, which has found that there is no evidence of a connection between reduced serotonin levels or activity and depression.
Professor Joanna Moncrieff, a Professor of Psychiatry at University College London and a consultant psychiatrist at North East London NHS Foundation Trust (NELFT), who led the research, says “it is always difficult to prove a negative, but 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.”
The idea that depression is caused by a serotonin deficiency has also provided the justification for the use of antidepressants. Antidepressants were originally said to work by rectifying serotonin levels. There is no other accepted pharmacological mechanism by which they affect the symptoms of depression. Therefore, this research calls into question reasons for the use of antidepressants.
Depression: An Imbalance in Chemicals?
For decades people have been told by doctors and by official information that their depression is caused by a chemical imbalance in their brains, particularly a lack of the brain chemical called serotonin. The vast majority of people have accepted this idea, with studies showing that 85-90% of the public believes that depression is caused by low serotonin or a chemical imbalance. This peer-reviewed, umbrella review of systematic reviews and meta-analyses led the authors to conclude that there is “no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations.”
These findings have important implications, the authors argue. The public overwhelmingly believes that depression is caused by low serotonin or other chemical abnormalities. This belief shapes how people understand their moods and has been shown to lead to a pessimistic outlook on the likelihood of recovery, and the possibility of managing moods without medical help. This is important because we now know that at least 85% of people will meet criteria for anxiety or depression at some point in their lives. It is possible that believing that low mood is caused by a chemical imbalance makes it more likely that people will become significantly depressed and less likely that people will make a good recovery.
Other studies show that the idea that depression is a result of a chemical imbalance also plays a role in people deciding whether to take an antidepressant and whether to continue taking it. People can be reluctant to stop antidepressants, even when they are no longer recommended, because they believe that they have a chemical deficiency in their brain.
Part of the reason why the story of chemical imbalances in depression has become so prevalent is because it was propagated by drug companies when they were marketing new antidepressants. Antidepressants have been blockbuster drugs for the pharmaceutical industry over the last few decades, frequently ranking among their most profitable drugs. The internet means that drug company marketing reaches a much wider audience than ever before.
The lack of evidence for lowered serotonin in depression has been increasingly recognised by psychiatric bodies, with the Royal College of Psychiatrists removing all reference to ‘chemical imbalances’ from their website in recent years. They now say in official statements that “the original idea that antidepressants ‘correct a chemical imbalance in the brain’ is an over-simplification.” However, some leading researchers still claim the serotonin theory is true, and psychiatric textbooks still give it extensive coverage. In contrast, this new research confirms that the serotonin theory of depression is not supported by science – even though for decades patients and the public have been led to believe it is true.
The Chemical Imbalance Theory is Profitable
The popularity of the chemical imbalance idea of depression has coincided with a huge increase in the use of antidepressants. Prescriptions for antidepressants have sky-rocketed since the 1990s, going from being rare to a situation now where one in six adults in England and 2% of teenagers are prescribed an antidepressant in a given year.
Dr Mark Horowitz, IIPDW Associate, training psychiatrist and Clinical Research Fellow in Psychiatry at University College London and NELFT, and an author on the study, 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.”
Prof Moncrieff added: “Epidemic proportions of the UK population are using antidepressants at the moment. Thousands of people suffer from their side effects, including the severe withdrawal effects that can occur when people try to stop them, yet prescription rates continue to rise. This situation has been driven by the promotion of the false belief that depression is due to a chemical imbalance. It is high time to inform the public that this belief is not grounded in science.”
This review was written by editors of International Institute for Psychiatric Drug Withdrawal
Original Article in Molecular Psychiatry
*Moncrieff, J., Cooper, R.E., Stockmann, T. et al. The serotonin theory of depression: a systematic umbrella review of the evidence. Mol Psychiatry (2022). https://doi.org/10.1038/s41380-022-01661-0
Access: https://www.nature.com/articles/s41380-022-01661-0#citeas First published: July 20, 2022