For centuries, doctors have struggled to define mental illness-how do you diagnose it, how do you treat it, how do you even know what it is? In search of an answer, in the 1970s a Stanford psychologist named David Rosenhan and seven other people—sane, normal, well-adjusted members of society—went undercover into asylums around America to test the legitimacy of psychiatry's labels. Forced to remain inside until they'd "proven" themselves sane, all eight emerged with alarming diagnoses and even more troubling stories of their treatment. Rosenhan's watershed study broke open the field of psychiatry, closing down institutions and changing mental health diagnosis forever.

But, as Cahalan's explosive new research shows, very little in this saga is exactly as it seems. What really happened behind those closed asylum doors, and what does it mean for our understanding of mental illness today?

This book contains many scientific concepts and ideas, as well as themes of violence and abuse.

Susannah Cahalan was not okay. Over the course of a month she went from being a fully functioning young reporter to suffering from psychosis and hallucinations, a step away from being diagnosed with schizoaffective disorder. In her devastating 2012 memoir, Brain On Fire, Cahalan details how a neurological disease not only caused her body to attack her brain, but also caused her to question her own sanity.

Susannah is fully recovered now, but what would have happened to her if her diagnosis of mental illness had stuck? This is what she grapples with in The Great Pretender, an engrossing history of the study of mental illness, centered around an experiment in which a psychiatrist and a group of other healthy people get themselves committed to mental hospitals in the early 1970s. There they experience the dehumanizing, traumatizing nature of the institutions themselves, and ultimately discover firsthand how mental illness diagnoses are biased and arbitrary at best.

How do we decide who is mentally ill? Drawing on years of archival research as well as her own personal experiences, Cahalan’s gripping account of the history of insanity is a feat of both enjoyable storytelling and skillful reporting.