Elevated serotonin levels drive synaptic plasticity, stimulating neurons in key brain regions to wire up. It's this increase in grey matter over weeks that is associated with better outcomes, particularly in PTSD.

This has been shown in several studies that use MRI before and after treatment, and explains the lag time.

That's correct - Serotonin is not the only factor. That still refutes the author's hypothesis that mental illness is some sort of personality defect.

Who’s asserting a personality defect? There are plenty of people whose depression stems from real, tangible issues in their present or past life. Solving these problems or, if they don’t actually have any active relevance to present life anymore, just processing them, has also been shown to be very effective. You don’t have to have a “defect” to have a problem.

Depression spirals and is self-perpetuating, so it has a nasty tendency to stick, but assuming that all depression only stems from a simple chemical imbalance, with no correlation to anyone’s life situation (again, past or presence) is very simplistic.

I’m not arguing for the article, but against the opposite view that all depression is rooted in chemical instead of psychological causes.

Our society considers it a personality defect because people suffering from mental health issues have behavior that deviates too far from the average.

It wasn't that long ago that people thought cancer patients were contagious.

Viral infections are thought to contribute to 15-20% of all cancers https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2267909/