The chemical-imbalance theory is weaker than commonly believed

Hari opens by interrogating the dominant public explanation for depression: that it's caused by a chemical imbalance in the brain, especially low serotonin, correctable by antidepressant medication. He reports that many of the researchers who originally studied serotonin's role are now far more cautious about this claim than the popular narrative suggests, and that the evidence for serotonin deficiency as the cause of depression is considerably thinner than decades of pharmaceutical marketing implied.

This matters personally for Hari, who had taken antidepressants for years, initially with relief, only to find the effect fading over time even as he stayed on and increased his dose — an experience, he discovers through his reporting, common enough that it has a name among researchers.

He's careful not to claim medication never helps anyone — it demonstrably does for some — but argues that treating brain chemistry as the whole explanation for depression, rather than one piece of a larger puzzle, has left many other real causes unexamined and untreated.

Takeaway: if antidepressants alone didn't fully work for you, that may reflect the theory's limits more than any failure of yours.