Sources: Molecular Psychiatry: The serotonin theory of depression: a systematic umbrella review of the evidence, Psychology Today: Depression Not Caused By Chemical Imbalance, Many Antidepressant Studies Found Tainted by Pharma Company Influence, Meta-analyses with industry involvement are massively published and report no caveats for antidepressants
In what might be the biggest rebuke of the Pharmaceutical Industrial Complex since they were forced to pay for the Opioid Crisis, a recent exhaustive umbrellas review of meta analyses reviews conducted by Joanna Moncrieff and associates at the University College London found that 'the major strands of research on serotonin shows there is no convincing evidence that depression is associated with, or caused by, lower serotonin concentrations or activity' and that 'Most studies found no evidence of reduced serotonin activity in people with depression compared to people without.' However, the review did find an avenue between traumatic life events and onset of depression (as exists for most mental disorders):
Moncrieff notes: “One interesting aspect in the studies we examined was how strong an effect adverse life events played in depression, suggesting low mood is a response to people's lives and cannot be boiled down to a simple chemical equation."
Their line of inquiry should also look into the link between diet and depression. As I noted 3 years ago in How Congress Created Our Obesity and Mental Disorder Epidemics much of the rise in mental disorders has been accompanied, in no small part, by the average American diet becoming more dependent on processed foods higher in refined sugars and saturated fats.
A recent study in the field of neuroscience has found that typical diets in Western countries, especially the United States, are linked not only to obesity and other physical diseases, but also mental health disorders such as depression, anxiety disorders, and dementia (Jacka, Cherbuin, Anstey, Sachdev, & Butterworth, 2015). A longitudinal study published in BMC Medicine Journal found that unhealthy dietary patterns, characterized by high concentrations of saturated fats and refined sugars and a lack of nutrient dense foods, are independently associated with smaller left hippocampal volumes in older adults compared with dietary patterns characterized by nutrient dense foods (Jacka et al., 2015).
And even before this umbrella review was conducted and published, it was publicly acknowledged that the so called science behind anti-depressants was heavily manipulated by the same companies who stood to profit from there sale. This much was uncovered in the wake of the Paxil scandal, an anti-depressant manufactured by GlaxoSmithKline and once marketed for children.
The latest study, published in the Journal of Clinical Epidemiology, which evaluated 185 meta-analyses, found that one third of them were written by pharma industry employees........... Almost 80 percent of meta-analyses in the review had some sort of industry tie, either through sponsorship, which the authors defined as direct industry funding of the study, or conflicts of interest, defined as any situation in which one or more authors were either industry employees or independent researchers receiving any type of industry support (including speaking fees and research grants). Especially troubling, the study showed about 7 percent of researchers had undisclosed conflicts of interest..........Although a third of the papers were written by industry employees; of the majority of authors, 60 percent were independent, university-affiliated researchers with conflicts of interest. For the 53 meta-analyses where the author was not an industry employee and did not report any conflicts of interest, 25 percent had unreported conflicts of interest that the researchers identified in their search and included in their evaluation.
Despite being exposed as a falsehood for which there is no clear and convincing evidence, companies like Pfizer and Eli Lilly are still poised to rake in record profits from the SSRI antidepressant market which is expected to grow at a compound annual rate of 3% over the next decade as the population of people with depression grows and more seek an easy solution in pill form.