Is the serotonin hypothesis dead? If so, how will clinical psychology respond?

For decades models of mental illness, particularly depression, have been influenced by the serotonin hypothesis (Coppen, 1967; Fakhoury, 2016). Specifically, that dysregulation in the serotonin neural system is an underlying biological cause of affective disorders. This model is the primary justification for the prescription of selective serotonin reuptake inhibitors (SSRIs; e.g., Prozac [Fluoxetine], Zoloft [Sertraline], Lexapro [Escitalopram]). SSRI prescription is extremely popular within modern psychiatry, with an estimated 13% of people living in the United States having taken an SSRI within the past 30 days (Brody and Gu, 2020). World-wide estimates are difficult to obtain, but developed European nations report commensurate prescribing activity (Abbing-Karahagopian et al., 2014), with indicators suggesting that SSRI prescriptions are increasing worldwide (Lockhart and Guthrie, 2011; Chen et al., 2022). Notably, estimates suggest the SSRI industry to be worth over $15 billion (USD) as of 2021 (Antidepressants Global Market Report 2021: COVID-19 Implications Growth to 2030, 2021)