Depression may not be linked to low levels of serotonin in the brain, new study finds

Since the 1960s, most scientists have agreed that the symptoms of depression are caused, among other things, by a chemical imbalance in the brain. For example, there is a dysfunction of certain neurotransmitters such as serotonin (also known as 5-hydroxytryptamine or 5-HT). Treatments for depression – such as selective serotonin reuptake inhibitors (SSRIs) – thus aim to “to increase the availability of serotonin in the brain”recalls New Scientist.

A recent analysis of seventeen studies, published on July 20, 2022 in the journal Molecular Psychiatry, however, challenges this scientific consensus. Carried out by researchers from University College London and led by psychiatrist Joanna Moncrieff, this research focused, among other things, on “the molecules found in the cerebrospinal fluid where serotonin is broken down” or “the levels of serotonin receptors and their degree of activity” in people with depression.

According to the researchers’ conclusions, there is no evidence that a low activity or amount of serotonin causes depression. “The conclusion of our article is that we do not know what SSRI antidepressants are used for”comments Joanna Moncrieff. “One possibility is that they act through a placebo effect.”

A controversial analysis

For other researchers, however, this new study has significant limitations. According to Johan Lundberg, of the Karolinska Institute (Sweden), the research carried out by Joanna Moncrieff does not report a distinction between people suffering from chronic depression and those who present depressive episodes, “whose condition at the time of assessment could affect the functioning of their serotonergic system”.

“It is essential to analyze data separately from studies that examine the same patients when they are sick and when they are in remission, in order to have optimal conditions for examining the hypothesis”argues Lundberg.

“It must be recognized that 5-HT is probably only one of the factors contributing to depression”says Paul Albert, neuroscientist at the University of Ottawa, Canada. “Given the strong placebo effect in the treatment of depression, it is likely that the contribution of other systems, in particular dopamine which is implicated in the placebo effect, is more important than that of 5-HT. »

On the side of the Royal College of Psychiatrists, which brings together eminent British psychiatrists, the specialists recall that “The effectiveness of antidepressants varies between people, and the reasons for this are complex”. Above all, the doctors urge the population to “don’t stop taking [leurs] antidepressants based on this study, and [encouragent] anyone with concerns about their treatment to contact their GP”.

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