From what I’ve read and understand on the topic, it seems there has been a critical media mistake on the interpretation of the meta research paper in question. My understanding is that the paper, using meta analysis, demonstrated that serotonin drugs do not work through what was once thought to be the active pathway for alleviating depression. IE through moderating serotonin levels in the brain. This does not disprove the theory that depression may be due to a chemical imbalance, nor that serotonin drugs are of no benefit for alleviating depression, only that they don’t work via moderating serotonin levels. Furthermore, drugs used for many other psychoactive and non psychoactive purposes, rely on moderating the levels of a variety of neurotransmitters, and other chemical compounds found in the human body. Therefore, these drugs, working through a multitude of chemical pathways exert their beneficial effects by influencing concentrations of chemical compounds in the human body. Therefore, it can be strongly argued that these compounds work by restoring, or creating a more benificial balance of chemicals, such as neurotransmitters.