At least for depression, the chemical imbalance theory has long been disproved, a recent summary of the evidence: https://www.theguardian.com/society/2022/jul/2

At least for depression, the chemical imbalance theory has long been disproved, a recent summary of the evidence: https://www.theguardian.com/society/2022/jul/20/scientists-question-widespread-use-of-antidepressants-after-survey-on-serotonin https://www.theguardian.com/society/2022/jul/20/scientists-q...