Johann Hari, the author, had endured years of depression before he visited a doctor. During consultations, the doctor asked Hari about his life and what could be improved. Finally, his doctor told the author that depression was due to a chemical imbalance in the brain. As a result, Hari started taking Paxil, which is a selective serotonin reuptake inhibitor (SSRI). This medication is supposed to normalize serotonin levels.

It wasn't until Johann Hari was 30 that he seriously started to think about the answers to questions about his life. The author delved into research on the connection between antidepressants and depression. He spoke with several researchers and found that there is little evidence to support the idea that a chemical imbalance in the brain causes depression. It is also impossible to prove the universal positive effects of SSRIs in treating depression.

Unfortunately, money is still more important than a healthy life. So, it's no surprise that the medical field also focuses on enrichment. Pharmaceuticals are a marketing industry. Their main goal is to promote a product based on research and release the medication to the market. British psychiatrist and researcher Joanna Moncrieff investigated this subject. Two types of depression are hard to distinguish: "reactive" depression, linked to the environment and life experiences, and "endogenous" depression, caused by issues in the brain. Yet, she states, "There’s no evidence that there’s a chemical imbalance."

Moreover, Harvard professor Irving Kirsch also investigated the connection between serotonin and depression. The American psychologist found that this connection was an "accident of history." In his view, scientists misinterpreted the results, leading pharmaceutical companies to produce and sell medications based on misinformation. Another example that he found was that 245 patients participated in Prozac clinical trials, yet the published results only mentioned 27 participants with positive outcomes. With Paxil, it was found that patients responded better to a placebo than to the medication. This proves that the main task of pharmaceuticals is to produce and sell medicines on the market.