Book Review: ‘The Age of Diagnosis’ by Dr. Suzanne O’Sullivan

Professor Andrew McDonnell reviews ‘The Age of Diagnosis: Sickness, Health, and Why Medicine Has Gone Too Far’ by Dr Suzanne O’Sullivan (2025).

In this new publication, Dr Suzanne O’Sullivan deals with a number of highly sensitive areas, including potential and misdiagnosis of a range of conditions such as ADHD, autism, cancer, and long Covid. Dr O’Sullivan, a consultant in neurology in London, presents a view that overdiagnoses of many conditions leads to a race for explanations and ultimately a lifelong medicalised pathway.

Whilst she acknowledges that diagnoses have a place in our society, she balances the area of self-diagnoses with conditions such as Huntington’s Disease, which has no cure. In many cases, people decide not to take genetic tests for conditions such as these.

Dr O’Sullivan also addresses the difficult issue of multiple overlapping diagnostic labels, such as ADHD and autism. In many diagnostic cases, you can determine a clear ‘Yes’ or ‘No’ answer. However, many conditions are not as clear cut, especially when it comes to mental health and neurodivergence. Similarly, we as humans are susceptible to bias, and may may interpret statements such as 1 in 2 people will develop cancer in their lifetime extremely negatively, forgetting the crucial point that 50% of people do not develop mutations.

In contrast to the medicalised model of diagnoses, Dr O’Sullivan makes a radical suggestion:

‘If our aim is to create a healthier population, there may be better ways to do it than early diagnosis and screening. Antibiotics, vaccines, insulin and blood transfusions have saved billions of lives. But even more lives have been saved by good sanitation, better nutrition and advances in agricultural technology.'

I would add, in my humble opinion, that fighting poverty and focusing on positive psychological factors such as well-being are necessary to improve health. 

The harsh reality is that we exist in a world where diagnosis provides access to resources. There are huge numbers of parents who await a diagnosis for their child on long waiting lists because this is opens up pathways to supports. I often wonder why we have a rationing approach to diagnosis, when surely a needs-based system would be ultimately better.In sum, I thoroughly recommend this book for anyone interested in this area. My take-away from this book is that medicine has limits, which should make us cautious. This book does not reject all diagnosis but highlights how error prone and biased we are.

The Age of Diagnosis: Sickness, Health and Why Medicine Has Gone Too Far https://g.co/kgs/NB6p8uH