If you have paid attention to the science of mental health, you will have heard the theory that depression is caused by a chemical imbalance in the brain. Since the 1990s, the common symptoms – low mood, loss of interest and pleasure, changed sleep and appetite – have been said to arise from a lack of a neurotransmitter called serotonin. By raising levels of this “happy hormone”, certain antidepressant pills such as Prozac could relieve our inner torment and return our minds to equanimity.
The truth, as ever, has turned out to be more complicated. Last year, an influential review of the available data concluded that there was no clear evidence to support the theory, and the ensuing headlines left many bewildered about who or what to believe.
