A study on the causes of depression sparks controversy

“Our study […] calls into question the basic idea behind the use of antidepressants”, affirmed the end of July the psychiatrists Joanna Moncrieff and Mark Horowitz on the site The Conversation, relaying a work published in the journal Molecular Psychiatry.

This study tackles the serotonin hypothesis. This suggests that depression is linked to a deficiency of this molecule involved in the transmission of emotions in the brain. The work, based on a compilation of previous publications and therefore a priori more solid than an isolated study, concludes that no link has been proven between a deficit of serotonin and the presence of depression in an individual. For its authors, it is a profound questioning of a hypothesis that has served for decades as a framework for numerous studies. The majority of current antidepressants have indeed been developed to act on serotonin levels.

But many critics quickly targeted this study and, even more, the presentation made by Joanna Moncrieff, a psychiatrist known for her skepticism towards biological explanations of depression, as well as her radical speech against the pharmaceutical industry.

“Serotonin” by Houellebecq

“Overall, I agree with the conclusions of the authors but I would not have such inflexible certainties”, commented the British psychiatrist Phil Cowen, in a reaction to the Science Media Center. The criticisms of Phil Cowen and other colleagues are of different orders. Some question the methodology of the study, in particular the fact of not measuring serotonin directly but an indirect trace of it; others accept his conclusions but reject their innovative character.

“No mental health specialist would currently support the idea that a pathology as complex as depression is explained by the deficit of a single neurotransmitter”, notes Phil Cowen.

The argument does not hold for Joanna Moncrieff, according to whom the serotonin hypothesis, even in a reduced version, still holds an important place in the discourse of psychiatrists. “And above all, even if eminent psychiatrists are beginning to doubt the links between depression and serotonin deficiency, no one has warned the general public”, ironically on her blog the author, who appears to be breaking with “psychiatry dominant”.

The links between depression and serotonin are, in fact, well anchored in popular imagery. In 2019, the French author Michel Houellebecq had thus titled “Sérotonine” a novel whose main character is depressive.

Effectiveness of treatments

But it is not the calling into question of the serotonin hypothesis that arouses the strongest criticism. It’s the fact that Joanna Moncrieff makes an argument against current antidepressants, going beyond the findings of her own study.

This “is a serious work, which is part of the continuation of other work and which counts in the discussion between experts concerning the mechanisms of depression”, admits the Swiss psychiatrist Michel Hofmann. “But I don’t think this is an article that should have a short-term impact on the prescription of antidepressants”.

Because for Joanna Moncrieff – who certainly warned that an antidepressant should not be abruptly interrupted at any price – we must necessarily doubt the benefits of treatments developed on the basis of a questioned hypothesis.

However, many psychiatrists, including Michel Hofmann, point out that the effectiveness of these treatments, whatever the root cause, has been scientifically assessed. “The mechanisms of the drugs used in the treatment of depression are generally multiple and finally, in most cases, we do not know precisely what makes the effectiveness of a treatment”.

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