We have been told for years that depression is likely to be caused by low serotonin (one of the ‘happy hormones’), sometimes described as a ‘chemical imbalance’. Joanna Moncrieff MD, a professor of psychiatry based at the University College London has recently analysed 17 historical studies and has come to the conclusion, alongside two other experts (Cooper and Stockmann), that this may not be the case. (Source *1)
Discovery of a Link Between Serotonin and Depression
In the 1960’s, there was a suggestion made that there is a link between low serotonin and depression (Source *2). Within that article back in 1967, the researcher even states that the study is ‘by no means conclusive’. However, the general public, and physicians too, have ‘run with it’ and it has now become popular belief amongst many that depression is caused by a chemical imbalance in the brain.
In 1987, Selective Serotonin Reuptake Inhibitors (SSRI’s), a form of anti-depressant, were introduced to the market. At that time, the narrative that depression is caused by a chemical imbalance was spread across the World in the form of marketing for these new drugs.
SSRI’s became a popular option to help people with depression and according to Public Health England (Source *3), 17% of the adult UK population were on anti-depressants in 2017-2018.
Where is the Evidence?
The evidence to support the link between low serotonin levels and depression is very weak. That is not to say that SSRI’s do not work (more on that later).
The workings of the human brain are very complex, and we are only really at the beginning of understanding it in its entirety. However, despite a multitude of studies having taken place, there remains no clear evidence of a link between low serotonin levels and depression. I have tried to find evidence for the sake of a balanced review and all sources have led me to the same conclusion.
Why SSRI’s Still Sometimes Work
Anti-depressants are used to change the chemistry in the brain, and they work for a lot of people. However, there is no clear evidence at the time of this publication that the change is due to the drugs directly targeting the depression. It’s role in changing the brain chemistry may be targeting the actual cause of the depression rather than the depression itself. That is one of the possibilities.
Another possible explanation could be the placebo effect. The placebo effect is a proven theory where people feel better having been given what they think is a beneficial drug during clinical trials. However, they are actually not given a drug when they are in a placebo group. They sometimes feel better because their mind ‘tricks’ them into believing they have received the beneficial drug.
This could certainly contribute to some of the cases where people have noticed an improvement in their mood following the intake of SSRI’s. It is unlikely that the placebo effect alone is causing so many people to feel an improved mood when taking SSRI’s though. There seems to be more going on, and more research is needed.
What is the Real Cause of Depression?
If depression is not caused by low serotonin levels as the new research indicates, then you may find yourself wondering what the actual cause is. This is such a huge question and the answer is so variable. There is not one answer to this question. Depression could be as a result of any of the following, and more:
- Physical health issues
- Inherited genetics
- Childhood difficulties
- Diet
- Alcohol
- Recreational drugs
- Prescription medication
- Lack of exercise
- A multitude of mental health problems
- Brain injury
- Poor sleep
- Life events
My Conclusion
The research paper talks about a chemical imbalance not necessarily being the cause of depression. By ’chemical imbalance’, they seem to be referring to low serotonin, but there are other chemicals that could be imbalanced that are not discussed in detail in this research paper.
My conclusion would be that it does seem from the evidence analysed that there is little evidence showing that low serotonin levels cause depression. However, the takeaway for me is that a lot more research needs to be done on the other chemical interactions that take place within the brain.
There are multiple chemicals in the brain. Although low serotonin may not be the cause of depression, it’s possible that other chemical imbalances within the brain might be. More research needs to be done on this to find out the true correlation between different chemical imbalances and depression.
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Source *2: Coppen A. The biochemistry of affective disorders. Br J Psychiatry. 1967;113;1237-64
Source *3: Public Health England. Prescribed medicines review: summary. 2018.