Intended for healthcare professionals

Observations Reality Check

Overdiagnosis and the dangers of early detection

BMJ 2011; 342 doi: (Published 23 February 2011) Cite this as: BMJ 2011;342:d1140
  1. Ray Moynihan, author, journalist, and conjoint lecturer, University of Newcastle, Australia
  1. Ray.Moynihan{at}

A new book calls for greater awareness of the potential harms of early diagnosis

How often it is in matters medical that the truth feels strange and counterintuitive, seduced as we are by so many false yet familiar assumptions: newer is better; widely used procedures are all proved; a registered drug must surely be a safe one. But perhaps the unhealthiest fallacy of all is the popular conviction that early detection is always for the best. A powerful new book from a team of Ivy League doctors claims that overdiagnosis is one of medicine’s biggest problems, causing millions of people to become patients unnecessarily, producing untold harm, and wasting vast amounts of resources.

Over-diagnosed: Making People Sick in the Pursuit of Health ( is written by three widely published researchers, Gilbert Welch, Lisa Schwartz, and Steve Woloshin. They’re all based at the Dartmouth Medical School in New Hampshire and known for rigour and scepticism. All three are practising doctors and scientists and are well aware that in many, many cases early diagnosis can ameliorate suffering and extend life. But as the evidence makes clear, too often conditions are being “overdiagnosed”: people are labelled with a condition that will never cause them symptoms or premature death. And, as the authors remind us, people whose conditions are overdiagnosed can never benefit from treatment, they can only be harmed.

The best known example is probably prostate cancer. Concern has been widespread for years that mass screening programmes may cause many men to be given a diagnosis and treated unnecessarily, sometimes with highly invasive and harmful procedures. In one of many chilling statistics drawn from the literature on screening the book states that, in the best case scenario, “for every man who avoids a prostate cancer death, roughly fifty are over-diagnosed and treated needlessly.” The number could be as high as 100.

Prostate cancer is also a powerful example of another wider problem: the weakness of commonly used tests such as the prostate specific antigen (PSA) test, which can uncover supposed “abnormalities” that result in great anxiety and further intervention but that may never develop into disease. From simple swabs to sophisticated, high tech diagnostics, we are constantly “seeing too much.” To illustrate the problem Over-diagnosed cites examples where expensive scans can produce inaccurate diagnoses, which in turn create the potential for unnecessary gallbladder, knee, and back surgery.

As I and others have written, many of the big and costly medical conditions of our time are not in fact diseases but rather are risk factors portrayed as diseases. The widespread promotion of preventive drugs for high blood pressure, high cholesterol, high blood sugar concentrations, and low bone mineral density is costing vast amounts of public resources globally, despite doubts about whether this is money well spent (Järvinen T, Sievänen H, Kannus P, Jokihaara J, Khan K, “Pharmacological disease prevention: is it cost effective?” BMJ, forthcoming).

Over-diagnosed charts how the definitions of these so called diseases have changed in recent decades, with boundaries being widened and treatment thresholds being lowered, dramatically expanding the number of people classed as patients simply because they’re at risk of future bad events. For example, broader definitions of high blood pressure brought a 35% jump in the number of people classed as sick, while a changed definition of high cholesterol meant that tens of millions more Americans became patients.

But, as people at lower risk are treated, the chances that those treatments will help them fall and the number of people you need to treat unnecessarily so as to help one person rises dramatically. As one graph in Over-diagnosed shows, if you treat people with severely high blood pressure for five years, the chance of preventing a bad event is almost 80%, thus you are helping almost everyone you treat. But for those with very mild hypertension the chance of benefit is closer to 5%, so 95% people are treated for five years without any benefit.

Another calculation estimates the value of taking lifelong drug treatment for mild or “near normal” osteoporosis. Only 5% of people with mild osteoporosis are saved from a fracture, so the other 95% are exposed to the potential harms of the drugs with no benefit. Given the side effects of popular osteoporosis drugs, which can include ulceration, osteonecrosis of the jaw, and atypical fractures, these figures are scandalous, adding weight to calls for a rethink of how we treat these risk based conditions and why we target so many healthy people with “preventive” drugs.

However, any rethink will need renewal of the expert panels that write definitions and guidelines, to free them of financial ties to drug makers, because, says Over-diagnosed, “these decisions affect too many people to let them be tainted by the businesses that stand to gain from them.”

A key theme here is the need to get better, clearer information to people—to get closer to the truth of the uncertainties around early detection and the potential harms of unnecessary treatment. Unlike so much promotion that passes for medical journalism, Over-diagnosed features success stories of patients who have explored the uncertainties and opted not to accept potentially unnecessary treatments.

Building processes for mandatory and meaningful informed consent into the very infrastructure of medicine could be a big win for people who don’t want to become patients needlessly—but will likely mean a rather large loss for those who benefit from treating them.


Cite this as: BMJ 2011;342:d1140


  • Competing interests: RM is the author of Selling Sickness and other books about medicalisation and has published articles with L Schwartz and S Woloshin.