'This book tackles one of the most important health issues of our time. It is brilliant, thorough and vital. Empowering for anyone who has ever come across health information, stories, or advice online - which is pretty much all of us.' --Prof. Daniel M. Davis, author of Self Defence: A myth-busting guide to immune health

'In a world where online medical opinions are fast and often dodgy, this is the perfect antidote.' --Prof. Kevin Fong

'Eye-opening and concerning. This book will hopefully influence how you access healthcare information and maybe think twice before you make (often complex) decisions about your body based solely on your social media feed.' --Prof. John Tregoning, author of Live Forever?

'This superb book is an essential guide to the wild world of internet health - a series of cautionary tales, brilliantly told, about the perils of health influencers and the messages they peddle.' --Chris van Tulleken, author of Ultra-Processed People

'This book is a much-needed prescription for the unregulated world of online health misinformation by an expert, who knows and understands what she is talking about. The influence we are all under now to buy products, tests and gadgets that often have no proven value for our health is terrifying for society and actually bad for our health. I'll be telling my patients to read this!' --Dr Ellie Cannon

'A compelling book by a top investigative medical journalist.' --Daily Mail

'In a world ever more obsessed with popularity, Deborah Cohen is that rare thing - a truth seeker. Razor sharp, prodigiously researched and written with a balance that is the hallmark of true intellect, Bad Influence is essential reading for anyone needing to navigate the increasingly murky interface between medicine and the online world which - let's face it - is all of us.' --Dr Gabriel Weston, author of Direct Red

'A timely and eye-opening investigation into how social media is reshaping the way we think about health... Bad Influence takes readers inside a world where personal narratives and viral trends have more power than peer-reviewed research... Essential reading for anyone with a social media account - or anyone who cares about the future of evidence-based medicine in an age of influence.' --Rebecca Coombes, Head of Journalism, British Medical Journal

'Bad Influence arrives at a moment when fascination with health, longevity and "optimised living" has never been greater... With a reporter's eye and a scientist's precision, Deborah dissects the interventionist claims of the wellness industry and exposes the shaky evidence underpinning it. Her diagnosis is uncomfortable but urgent: that those selling us control over our health may, in fact, be the ones making us sick. Bad Influence is a must-read for anyone who has ever turned to the internet in search of better health - and a timely warning about the seductive power of bad influencers.' --Natasha Loder, Health Editor, Economist

'Exhaustively researched - documents the tensions between amazing modern medicine and twenty-first-century quackery. An important reminder of how technology's tentacles are reaching into every corner of our lives, and the challenge to work out what's real.' --Laura Kuenssberg

'This fascinating and simultaneously terrifying dive into 21st-century healthcare should be mandatory reading in 2026... you will read this book and become instantly better informed, self-aware and outraged.' --Stylist, Best Non-Fiction to Read in 2026

'Her [Deborah Cohen's] deeply reported, compelling analysis lays bare how social-media influencers, apps, algorithms and the rest of the digital ecosystem are transforming our health, for better or - often - for worse... Bad Influence is an essential read for anyone adrift in the ocean of conflicting online health claims - so basically, all of us.' --Nature