I linked to a paper published and written by several psychiatrists and psychologists that explains the history of the monoamine hypothesis, and why it's not a good theory. Why would they spend so much time debunking a theory nobody believes?
Quoting directly from the article
> Despite decades of research, the role serotonin plays in depressive phenotypes has not been conclusively determined. The original clue that monoamines (serotonin, norepinephrine, and dopamine) were involved in depression came from two serendipitous discoveries (Baumeister et al., 2003; Valenstein, 1998). First, during the investigations of iproniazid as a treatment for tuberculosis and imipramine as a treatment for schizophrenia, clinicians reported that these drugs could reduce depressive symptoms. An effort was then made to find a common pharmacological property that could explain their antidepressant effect. Eventually, researchers found that iproniazid inhibits the enzymes that break down the monoamines, while imipramine blocks the serotonin transporter (SERT) and the norepinephrine transporter (NET). Second, clinical observations suggested that reserpine, a drug known to deplete monoamines, increased depressive symptoms. These findings appeared to solve the puzzle. By preventing the breakdown of norepinephrine and serotonin, or preventing their clearance from the synapse, iproniazid and imipramine appeared to increase forebrain monoamine levels.
> The monoamine-enhancing effect of antidepressant medications (ADMs), coupled with the depression-inducing effects of reserpine, suggested that depression was caused by reduced monoamine neurotransmission (Everett and Toman, 1959; Jacobsen, 1964; Schildkraut, 1965)
Additionaly, this is something that lots of undergraduate psychology textbooks still mention as a potential explanation (one of mine did ~6 or 7 years ago, although at least they said that it was an implausible theory).
Quoting directly from the article
> Despite decades of research, the role serotonin plays in depressive phenotypes has not been conclusively determined. The original clue that monoamines (serotonin, norepinephrine, and dopamine) were involved in depression came from two serendipitous discoveries (Baumeister et al., 2003; Valenstein, 1998). First, during the investigations of iproniazid as a treatment for tuberculosis and imipramine as a treatment for schizophrenia, clinicians reported that these drugs could reduce depressive symptoms. An effort was then made to find a common pharmacological property that could explain their antidepressant effect. Eventually, researchers found that iproniazid inhibits the enzymes that break down the monoamines, while imipramine blocks the serotonin transporter (SERT) and the norepinephrine transporter (NET). Second, clinical observations suggested that reserpine, a drug known to deplete monoamines, increased depressive symptoms. These findings appeared to solve the puzzle. By preventing the breakdown of norepinephrine and serotonin, or preventing their clearance from the synapse, iproniazid and imipramine appeared to increase forebrain monoamine levels.
> The monoamine-enhancing effect of antidepressant medications (ADMs), coupled with the depression-inducing effects of reserpine, suggested that depression was caused by reduced monoamine neurotransmission (Everett and Toman, 1959; Jacobsen, 1964; Schildkraut, 1965)
https://sci-hub.st/https://www.sciencedirect.com/science/art...
Additionaly, this is something that lots of undergraduate psychology textbooks still mention as a potential explanation (one of mine did ~6 or 7 years ago, although at least they said that it was an implausible theory).