Clinical depression is one of the most common mental illnesses, according to the World Health Organization (WHO), about 280 million people are living with depression, and although several risk factors contribute to depression, there is a common idea that it is related to depression. with chemical imbalances in the brain, particularly with low levels of serotonin.
However, an article in which researchers analyzed 17 studies suggests that there is no evidence to support the idea, calling into question the theory of chemical imbalance, which originated in the 1960s, when it was observed that certain drugs had, as side effects, of its functions, positive effects on mood.
“It’s always difficult to prove a negative, but I think we can safely say that, after extensive research conducted over several decades, there is no convincing evidence that depression is caused by serotonin abnormalities,” said Joanna Moncrieff, lead author. from 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 is not linked to depression, what causes it?
The article offers no alternative explanation, but several experts point out that depression is a complex condition with multiple causes.
For the psychiatrist Guida da Ponte, from Centro-Hospitalar Barreiro-Montijo, this study “was reductive in the basis of her investigation and ended up being limited to the research of serotonin levels in depression, knowing that, in psychiatry, the etiology, the cause , of depression is not just an imbalance in neurotransmitters”, and points out that, “factually, this is not what the scientific community argues – that depression only has to do with serotonin levels”.
The psychiatrist also clarifies that depression is “a pathology of multifactorial etiology, with several risk factors”, and that, “as in any other area of medicine, it has to do with the individual, his own biology, his way of be, the way we were born, our personality, the impact of society on our biology, genetic factors that are well described, and then stressful life events – something that is interpreted by the patient as traumatic”. “I won’t say traumatic in the sense of intensity, but we call it a stressor, it causes discomfort, a disturbance”, she clarifies.
One of the areas of research included in Moncrieff’s review was investigation comparing serotonin levels and breakdown products in blood or brain fluid and, in general, indicated no difference between depressed and non-depressed individuals. 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 to 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 of a biochemical basis for depression”, and consider this “consistent with research on many other biological markers”, concluding that “it is time to recognize that the serotonin theory of depression is not empirically substantiated.”
Is it then safe to conclude that serotonin is not involved in depression?
In statements to Renaissance, psychiatrist José Tropa states that one cannot “refute this theory outright”, but neither can one “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 actually changes, not only in serotonin, but also in noradrenaline and dopamine, which are involved in the genesis and also in the evolution of the appearance of some symptoms of depression”.
However, the psychiatrist explains that there are still studies underway to understand how “this serotonin is involved”, and “some show that it has to do with serotonin precursors from a chemical point of view, such as tryptophan”. This imbalance, he says, can be present in certain patients, also remembering that “depression cannot be considered 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 says.
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