Clinical depression is one of the most common mental illnesses, according to the World Health Organization (WHO), about 280 million people live with depression, and although several risk factors contribute to depression, there is a common idea that it is linked to chemical imbalances in the brain, particularly low levels of serotonin.
Although, an article in which researchers analyzed 17 studies, suggests there is no evidence to support the idea, challenging the chemical imbalance theory, which originated in the 1960s, when it was observed that certain drugs would have, as a side effect of their functions, positive effects on the mood.
“It is always difficult to prove a negative result, but I think we can say with certainty that after extensive research over several decades, there is no convincing evidence that depression is caused by serotonin abnormalities” , said Joanna Moncrieff, lead author of the study. and book “The Myth of the Chemical Cure” [O Mito da Cura Química, em português] and Professor of Psychiatry at University College London.
But if, as the new study claims, serotonin isn’t linked to depression, what is causing it?
The article offers no alternative explanation, but several experts point out that depression is a complex disease with multiple causes.
For the psychiatrist Guida da Ponte, of the Centro-Hospitalar Barreiro-Montijo, this study “was reductive in the basis of its investigation and ended up being limited to the search for serotonin levels in depression, knowing that in psychiatry, the etiology, the cause, of depression is not just an imbalance of neurotransmitters,” and points out that, “in fact, that’s not what the scientific community argues – that depression has to do with serotonin levels.
The psychiatrist also specifies that depression is “a pathology of multifactorial etiology, with several risk factors”, and that, “as in any other field of medicine, it has to do with the individual, his own biology, his way to be”. , how we are born, our personality, the impact of society on our biology, well-described genetic factors, and then stressful life events – something that is interpreted by the patient as traumatic”. “I wouldn’t say traumatic in the sense of intensity, but it’s called a stressor, it causes discomfort, a disturbance,” he says.
One of the areas of research included in Moncrieff’s review was a survey comparing serotonin levels and breakdown products in blood or brain fluid and, in general, indicated no difference between depressed individuals and not depressed. The authors also analyzed studies, where serotonin levels were artificially reduced in hundreds of people, and concluded that the reduction in serotonin did not translate into the development of depression in healthy volunteers.
In the article, the researchers suggest that “the enormous research effort based on the serotonin hypothesis has not produced convincing evidence for a biochemical basis for depression”, and consider this “consistent with research on many other biomarkers,” concluding that “it’s time to acknowledge that the serotonin-based theory of depression is empirically unfounded.
Is it then safe to conclude that serotonin is not involved in depression?
In statements to Renaissance, Psychiatrist José Tropa asserts that we cannot “purely refute this theory”, but neither can we “establish a causal link between the chemical alteration of a neurotransmitter, in this case serotonin, and depression”. However, he adds, “there is evidence that there are indeed modifications, not only of serotonin, but also of norepinephrine and dopamine, which are involved in the genesis and also in the evolution of the appearance of certain symptoms of depression”.
However, the psychiatrist explains that there are still studies in progress to understand how “this serotonin is involved”, and “some show that it has to do with precursors of serotonin from a chemical point of view, such as tryptophan”. This imbalance, he says, can be present in some patients, also recalling that “depression cannot be considered as a simple disease, with a single cause”.
“In addition to being a syndrome, it is a set of symptoms, there are many types of depression and the causes are multifactorial”, he specifies.