THE MUST-READ BESTSELLER AND BOOK OF THE YEAR IN THE GUARDIAN, SUNDAY TIMES, FINANCIAL TIMES, ECONOMIST, NEW SCIENTIST AND MORE

'Revelatory. Slices through the contradictions.' - CHRIS VAN TULLEKEN
'So well-written... critically important.' - RANGAN CHATTERJEE
'A doctor's brilliant study of the dangers of overdiagnosis' - GUARDIAN

From autism to allergies, ADHD to long Covid, more people are being labelled with medical conditions than ever before. But can a diagnosis do us more harm than good?

The boundaries between sickness and health are being redrawn.

Mental health categories are shifting and expanding all the time, radically altering what we consider to be 'normal'. Genetic tests can now detect pathologies decades before people experience symptoms, and sometimes before they're even born. And increased health screening draws more and more people into believing they are unwell.

An accurate diagnosis can bring greater understanding and of course improved treatment. But many diagnoses aren't as definitive as we think. And in some cases they risk turning healthy people into patients.

Drawing on the stories of real people, as well as decades of clinical practice and the latest medical research, Dr Suzanne O'Sullivan overturns long held assumptions and transforms how we think about illness and health.

'Compassionate and bracingly independent thinking' - THE TIMES
'Exceptional. Chapter by brilliant chapter, it raises fundamental questions we should all be asking.' - NEW STATESMAN

*As heard on Radio 4 Book of the Week, Today, Good Morning Britain, Sky News and more.*

"O'Sullivan is brave to take this subject on, and she hits the target... she is an excellent, fluid writer, and an eloquent speaker... In a world where medical misinformation and disinformation flourish, and people die as a result, it takes courage to counter them without pandering to stereotypes. But that is what The Age of Diagnosis does so well... Its overall message is clear: diagnosis is a tool to be wielded with the utmost caution, and tolerance for difference and for imperfection can go a long way in keeping us healthy." - The Guardian

"'Exceptional... Chapter by brilliant chapter, [The Age of Diagnosis] raises fundamental questions we should all be asking when thinking about illness, be it cancer or genetic disorders, never shying away from difficult truths.'" - New Statesman

"'The neurologist takes eloquent aim at a medical culture that, although well intentioned, is too quick to assign clinical labels to aspects of the human condition... A brave and compassionate book.'" - Financial Times, best summer books of 2025

"A humane and thoughtful observer of the oddities of the human mind... full of intriguing case studies and wise observations. Her new book ranges widely, taking in the drawbacks of mass screening for illnesses as well as the perils of overextending mental health categories... We make people sicker by by the simple act of diagnosing them with a medical problem. A fascinating book." - The Times

"The neurologist Suzanne O'Sullivan has written insightful books about psychosomatic conditions. Here she turns her attention to the perils of over-diagnosis - including autism, allergies, ADHD and long Covid. Be prepared for compassionate and bracingly independent thinking." - The Times books to look out for in 2025

"Two elegant offerings from neurologists stand out for using patient stories to tell us something about ourselves. Suzanne O'Sullivan courageously questions medicine's well-intentioned enthusiasm for attaching labels - think ADHD, anxiety - to aspects of the human condition. This is sensitive political territory, given the public conversation about the 2.8m people who are economically inactive due to long-term illness, but it deserves a hearing." - Guardian, Best Books of 2025

"'O'Sullivan impressively marshals evidence of how drivers of 'overmedicalisation' have arisen, the minimal benefits conferred and the harms that can result. Most striking is her examination of the explosion in diagnoses of mental health conditions, such as autism and ADHD... O'Sullivan seeks out the 'reality' behind appearances, though her scepticism is tempered with sympathy and understanding... So entrenched has overmedicalisation become that there now seems no prospect of its being reversed. O'Sullivan's masterful diagnosis of how this has come about is immensely persuasive.'" - Literary Review