Known as the Rosenhan experiment, in 1973 psychologist David Rosenhan enlisted eight mentally healthy people who posed as patients with fictitious symptoms to see if they would be diagnosed as mentally ill and admitted to psychiatric hospitals.
Once admitted, the participants acted normally and reported that their symptoms had disappeared, yet they were not released until they agreed with the doctors' diagnoses and agreed to take antipsychotic medication. The experiment was widely publicized and raised concerns about the reliability and validity of psychiatric diagnosis and the treatment of mental illness.
Susannah Cahalan's "The Great Pretender" describes the historical experiments that sought to expose the flaws of psychiatric diagnosis, and the unethical practices of the study's leader, David Rosenhan, and the questions of the power dynamics between doctors and patients.
The therapeutic value of mental heath treatment is clear. It's use as a diagnostic, less so.