Since the 1960’s people have been led to believe that the root cause of depression was due to an imbalance of chemicals in the brain, specifically Serotonin. The latest UCL review reveals that there is no scientific or practical evidence of this, and points rather to negative life experiences being mostly responsible for the condition.
The Serotonin Theory
There is massive debate around the serotonin theory of depression, but it still has a profound impact on how the majority view the disorder, and on the treatment it receives. The theory is widely publicised, as well as taught as part of the Psychiatry curriculum worldwide, and as such is endorsed by leading professionals in the field as well as by official institutions.
The Serotonin chemical is a type of neurotransmitter that facilitates the transmission of information from one nerve cell to the next and plays a fundamental role in mood, appetite, and sleep as well as other key aspects of normal functioning.
There has been copious experimental research based on this biological theory, and it is from the main threads of this research that Joanna Moncrieff and colleagues at UCL have collated the systematic umbrella review in question. One of the co-authors, Mark A Horowitz, is quoted to have stated that ‘The vast sums of money spent on looking for the chemical equation of low mood might be missing the forest for the trees’.
The hypothesis that depression is the result of an irregularity of chemicals in the brain, serotonin in particular, has promoted the use of antidepressants to treat the condition. This escalated in the 90s when SSRI’s (Selective Serotonin Reuptake Inhibitors) were conceived. During this time there was a massive push by pharmaceutical companies endorsing the serotonin theory.
SSRI’s work by preventing the decrease of serotonin levels for a limited time and presently they are prescribed to one in six adults in the UK based on the belief that certain chemicals in the brain cause or promote the symptoms of depression.
Clearly antidepressants can work but it is evident that they are working in an altered way to what is popularly believed. The results of these recent findings, however, indicate that it is impossible to conclude that using SSRI’s is advisable as they may not even be safe.
The UCL Review
The intention of this study was to indubitably establish the nature of the connection between serotonin and depression and determine whether there is indeed evidence linking a lack of serotonin, or any chemical imbalance, to the aetiology of depression. Published on 20 July 2022 in the open access journal of Nature Molecular Psychiatry, the review concludes that there is a lack of scientific evidence to support the theory that lower serotonin levels cause depression or is even associated with it. This throws a much-needed light on the debate concerning the foundation of the use of anti-depressants.
Contrary to what is widely believed, studies have revealed that many people using, and even those that previously used, anti-depressants register a lower level of serotonin. Similarly, one would think that depression being a biological disorder would make it more ‘acceptable’ but it turns out to be exactly the opposite, and it also leads people to have a pessimistic view about their chances of recovery without using medication.
Other research has also shown that they are not much different from a placebo or that they seem to have a numbing effect on people’s emotions. Most importantly, in the majority of cases, there was no difference in the serotonin levels between healthy participants and those diagnosed with depression, and several studies where serotonin levels were artificially reduced in participants proved that it did not make them depressed.
The cause of depression is yet to be absolutely resolved but is most strongly linked to stressful and destructive life events as well as intolerable conditions such as discrimination and poverty.
The researchers say that it is not correct to tell patients that depression is caused by a chemical imbalance and that SSRI’s can correct the condition, but rather that a holistic approach starting with talking therapies should be utilised.
Experts in the field have responded by saying that while some important points are raised, and even though it is clear that the source of depression could rise from multiple factors, it does not mean that people should stop using their medication, as this has also proved to be dangerous. They also say that more research is required to substantiate some of the paper’s lofty claims which challenge popular belief.
Some have urged people to use the logic that using any specific medication does not necessary indicate low levels of the active ingredient in the body, but that they are still effective at treating the specific condition.
One thing is sure and that is that there is no clear evidence that low serotonin levels are the cause of depression.
https://www.nature.com/articles/s41380-022-01661-0#Sec5 <- the review in question