A BOOK with the title “Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition” does not sound destined to be a bestseller, particularly at $199 a pop. But DSM-5, as it is known for short, is almost certain to become one. Its predecessor, DSM-IV, which was published in 1994, has sold more than 1m copies. DSM-5, which will go on sale on May 22nd, is likely to do at least as well.

The reason is that the DSM series, which is published by the American Psychiatric Association (APA), has become the global standard for the description of mental illness. Indeed, the DSM is treated by many people less as a medical handbook and more as holy writ. Insurers use it to decide whether or not to cover ailments. And diagnoses based on it determine whether people get special services at school; whether they qualify for disability benefits; whether they are stigmatised in their careers; even whether they are able to adopt children. Doctors, patients, drug companies and insurers have all thus been waiting for the latest edition of what has become known as the psychiatric bible.

The DSM’s purpose is to set strict criteria for identifying mental disorders. This is supposed to make diagnoses more reliable: a laudable aim. To that end, more than 1,500 experts have spent over a decade labouring. In doing so, though, they have succeeded in adding to, rather than subtracting from, criticism that the DSM has become a monster. In the eyes of many critics it is a vehicle for misdiagnosis, overdiagnosis, the medicalisation of normal behaviour and the prescription of a large number of unnecessary drugs.

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