The Age of Diagnosis

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



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.


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

Review

The Age of Diagnosis covers so many topics that have been troubling me but which I hadn't been able to resolve myself. It slices through the confusion and the contradictions that have tied me in knots - both as a parent and as a clinician - with grace, elegance and compassion. It is scholarly and human, but an absolutely absorbing read from start to finish. There are very few people who could write this so straightforwardly and yet with endless compassion. I really cannot say good enough things about it. -- Chris van Tulleken, author of ULTRA-PROCESSED PEOPLE

Wow... So well-written, there's deep compassion behind the words... raising awareness of something critically important. -- RANGAN CHATTERJEE

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. -- Adam Rutherford ― 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.' -- Hannah Barnes ― 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

How does she carry off that high wire act, being so technical and expert and grounded in data, while telling stories in a way that makes them utterly addictive? I love the way she listens to people talking. It's a really important, intelligent, compassionate and brave book, and it speaks very eloquently to things happening in our ideas about ourselves. -- Tessa Hadley

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. -- Robbie Millen ― The Times

About the Author

Dr Suzanne O'Sullivan has been a consultant in neurology since 2004, first working at The Royal London Hospital and now as a consultant in clinical neurophysiology and neurology at The National Hospital for Neurology and Neurosurgery, and for a specialist unit based at the Epilepsy Society. She specialises in the investigation of complex epilepsy and also has an active interest in psychogenic disorders. Suzanne's first book It's All in Your Head, won both the Wellcome Book Prize and the Royal Society of Biology Book Prize and The Sleeping Beauties was shortlisted for the Royal Society Science Book Prize. She is from Dublin, Ireland.