It all started with a single category in the 1840 US Census: "idiocy/lunacy", with the first DSM appearing in 1952 (Diagnostic and Statistic Manual of Mental Disorders). Now there are hundreds of ways for us not to be 'normal'. Frances Allen, the psychiatrist who led DSM-4, has written a scathing critique of DSM-5 that has even more diagnoses: meet Disruptive Mood Dysregulation Disorder, folks (formerly known as temper tantrums).
Read more about psychiatric over-diagnosis in my guest blog at Scientific American: "Is anybody sane here?" said the psychiatrist to the journalist.
Find out more about tackling this problem in medicine generally at Preventing Overdiagnosis: Winding back the harms of too much medicine.
More of my cartoons on over-diagnosis: You have the right to remain anxious and The over-abundance of over-diagnosis.
[Update] In 2016, another look at the history of the DSM, with another call for the next one to be based on an objective assessment of reliable evidence.