Depression is a mood disorder characterized by persistent sadness, loss of interest or pleasure, and disruptions in thinking, energy, or daily functioning that interfere with one’s ability to carry out daily activities. For years, depression was widely believed to result primarily from a “chemical imbalance” related to serotonin. However, a major umbrella review in the early 2020s found no consistent evidence that low serotonin levels cause depression—helping explain why many patients experience limited improvement from selective serotonin reuptake inhibitors (SSRIs) or serotonin–norepinephrine reuptake inhibitors (SNRIs). As a result, researchers have shifted toward a broader understanding of depression, including the possibility…
