The article presents a possible explaination for why SSRI antidepressants (which increase the amount of serotonine in one's synapsis) are effective: serotonine

The article presents a possible explaination for why SSRI antidepressants (which increase the amount of serotonine in one's synapsis) are effective: serotonine plays a role in how we learn, and > [people with an] atypical function of the serotonin system may be at risk of developing depression or anxiety because they are too good at learning about negative outcomes > Serotonin changes produced by the drug, combined with appropriate therapy, might work by allowing patients to learn that the world is not such a bad place rather than simply making them happy. The article continues noting that this would explain a few things, like > (1) why treatment with SSRI anti-depressants doesn’t tend to increase happiness until weeks after depressed patients have begun taking medication. Serotonin changes produced by the drug, combined with appropriate therapy, might work by allowing patients to learn that the world is not such a bad place rather than simply making them happy. > (2) why some depressed patients generally do not improve when undergoing SSRI treatment. Consuming pills in the absence of improvement in life conditions or appropriate therapy might in fact make it easier for already depressed individuals to ‘learn’ more about the negative events surrounding them > (3) [why we] have no evidence that [simply] increasing brain serotonin levels actually improves people’s mood. The evidence shown to supports this role of serotonin in the learning process consists of two studies (cited in the article). The first showing that rats grown in the dark developed abnormal sensitivity to non-visual stimuli, and that serotinine played a role in the process. The second found that individuals with a particular genotype affecting the serotonin system were more likely than others to develop depression or anxiety only if they had experienced stressful life events. Betteridge's law of headlines checks out: Is serotonin the happy brain chemical? No, it (probably) plays a complex role in how we learn about bad outcomes.