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TIFFANY MCLEOD followed the advice to the letter. She has food allergies, and was worried that her children might too. Her doctor recommended that she avoid eating nuts while pregnant or breastfeeding, and to keep the kids away from them until the age of 3. 鈥淵ou want to do what鈥檚 best for your child,鈥� she says. 鈥淎nd you figure that your doctor knows what that is.鈥�

Her doctor was following American Academy of Pediatrics guidelines issued in 2000. But by 2008, the AAP had . Then last year, it reversed course. A large study had found that regular exposure to peanuts from 4 months of age . McLeod, who lives in Texas, had both of her babies in the years between the changing advice. She learned the hard way that her youngest has a life-threatening allergy. 鈥淲e had to rush her to the emergency room. It was extremely scary,鈥� she says.

It would be comforting to think the drastic change in advice with peanut allergy is unique. But this type of medical about-face isn鈥檛 rare. A recent analysis of research published in one medical journal over 10 years identified a whopping . To be clear, this is not just the process of upgrading advice as better evidence comes in. These are practices that became routine before we learned they didn鈥檛 actually work. And worse, before we knew if they could cause harm.

In the era of evidence-based medicine you might assume most of your doctor鈥檚 advice is based on evidence obtained through rigorous testing. But it is becoming clear that is often far from the case. Fortunately, people are now shining a light on the problem, and devising ways to fix it.

They have their work cut out. In recent years official advice has reversed course on everything from broad issues such as diet and nutrition, to specific techniques like using stents to keep open the narrowed arteries of people with heart disease. There have also been dramatic U-turns on cancer screening and other major public health concerns.

What is at stake

For many of us, this isn鈥檛 an abstract worry. My mother was given hormone replacement therapy (HRT) in the 1990s to help ease her way through menopause. That was before it was found to . Nine years later, when she was diagnosed with bilateral breast cancer, and endured a gruelling year of surgery and treatment, we were left wondering if or how much HRT had contributed to her disease.

鈥淭he medical journals are filled with interesting ideas that get tested and fail. That鈥檚 science,鈥� says at the University of Chicago, who wrote a book called with Vinay Prasad. 鈥淭he problem is when that new technology or treatment or surgery has actually gotten out and is being given to millions of people before it鈥檚 found to not work.鈥�

How does this happen? In the late 1990s, peanut allergies were on the rise and . At the time, the best theory about the cause was that feeding allergenic proteins to infants before the intestinal lining was mature allowed them to seep into the bloodstream. The baby then built up antibodies to these substances and later became allergic to foods containing them. This hunch was consistent with assumptions about how allergens affect the immune system, and studies showing few peanut allergies in countries where people don鈥檛 eat many peanuts. So steering clear of the potential allergens until children were older made sense 鈥� in theory.

鈥淢uch of what we do in medicine is theory-based. It鈥檚 only relatively recently that good quality evidence has been available for many things,鈥� says , who develops guidelines for the American Board of Pediatrics (ABP) and is a long-time campaigner for evidence-based practice. 鈥淧eanut allergy is life-threatening 鈥� we were doing the best we could with the knowledge we had at the time.鈥�

But no data backed up that theory. And now it seems just the opposite is true: exposure to peanut protein while the immune system is immature actually decreases the likelihood of developing an allergy.

鈥淲e spend so much time training people first and foremost in how the body works and how it breaks. So we get why things should work, and then we tend to adopt things because they should work before we know if they actually do,鈥� says Cifu.

It鈥檚 no small concern. An of 3000 common medical practices categorised half as having 鈥渦nknown effectiveness鈥�, and 3 per cent as likely to be ineffective or harmful. Just a third were found to be 鈥渂eneficial鈥� or 鈥渓ikely to be beneficial鈥�.

A major problem is that we often do the studies only after practices are widely adopted. There is a well-trodden path to developing new treatments, says , a medical historian at Harvard University. Someone gets some promising early results, a lot of people get enthusiastic about the innovation and get on board. 鈥淭hen it is successfully marketed to a willing audience of patients who are generally dissatisfied with existing treatments,鈥� says Jones.

Eventually, concerns surface and clinical trials are done. By then, though, the horse is out of the barn. People want innovation and ready access to new and better treatments. But, as Jones says, 鈥渋t leaves open the door that you鈥檒l get a lot of enthusiasm coming from small, poorly designed studies that drive unwarranted use of a new procedure before it has been fully validated.鈥�

It鈥檚 tough to get the horse back in the barn. For instance, a treatment known as vertebroplasty, which involves injecting medical cement into broken vertebrae, is widely used for people with spinal fractures related to osteoporosis. In spite of that it is , the practice is still used, even at , one of the top ranked hospitals in the US.

鈥淥nce a treatment has been dubbed 鈥榮tandard of care鈥� it tends to persist,鈥� says at Harvard Medical School, who studies the placebo effect. It isn鈥檛 that doctors are wilfully ignoring the evidence, it is likely they believe in what they鈥檙e doing. 鈥淭he practitioners who perform vertebroplasty want to help people and probably continue to believe they are doing so,鈥� he says.

Preventing untested practices from becoming standard care seems simple 鈥� just test them first. But even when studies are conducted early on, what they actually measure can be part of the problem. Because it鈥檚 simpler and faster, researchers often look at 鈥渟urrogate outcomes鈥�, not actual end points. So for instance, blood cholesterol levels are taken as a stand-in for the risk of heart attack or death.

Measuring what matters

For years, dieting and taking medication to keep a certain measure of blood sugar 鈥� glycated hemoglobin 鈥� below 7 per cent, was recommended for people with type 2 diabetes. This was after a with levels closest to those of non-diabetics had the best outcomes. But in 2008 a team led by at McMaster University in Ontario, Canada, discovered that those fighting to get their glycated haemoglobin below this threshold actually faced a .

鈥淭here comes along some piece of evidence that is definitive, so much better than the existing evidence, that you have to do a total 180 on something you once thought was the best way to go,鈥� says , an oncologist at Oregon 午夜福利1000集合 and Sciences University.

鈥淲e adopt things because they should work before we know if they actually do鈥�

The calibre of evidence can depend on who is paying for it. There are the perennial issues that plague medical research: the pressure on researchers to publish new and impressive findings, and medical journals鈥� tendency to publish positive results more than negative. But increasingly, the pharmaceutical and medical device industries 鈥� rather than public bodies 鈥� . Not only do they have vested interests in the initial outcomes needed to get drugs or devices approved, but once they are approved, little incentive to do the expensive, large-scale studies that could potentially upend their initial findings and hurt their bottom line.

The popularity of the anti-inflammatory drug Vioxx is one example. The US Food and Drug Administration (FDA) approved it in 1999, but later the manufacturer, Merck, was accused of concealing risks discovered in early studies. By the time independent research showed that , 20 million people had prescriptions. It was , but not before causing up to 140,000 preventable heart attacks. Merck pleaded guilty to criminal charges in 2011 and .

There is no simple fix. There are so many factors at play, and for some, there is no perfect way 鈥� this is what progress looks like.

鈥淭here are cases where we just haven鈥檛 done the research we need to do before a practice gets adopted,鈥� says Moyer. 鈥淏ut there are also a whole host of reasons why the evidence for certain medical practices might change 鈥� and continue to change 鈥� over time.鈥�

Among them is the fact that you鈥檙e often working on a moving target. 鈥淒iseases aren鈥檛 static 鈥� they can and do change over time,鈥� says Gerstein. 鈥淒iabetes today is not the same as it was 50 years ago.鈥� The number of people diagnosed with type 2 diabetes has more than doubled in the past two decades, and the age of onset has dropped. He says today鈥檚 type 2 diabetes is more likely to come with additional health issues like cancer, kidney problems and heart disease, compared with 50 years ago. 鈥淲e call it by the same name but it behaves differently,鈥� says Gerstein.

So where do we go from here? It is understandable that patients and their advocates want new options as soon as possible, especially those who are seriously ill. At the same time, it makes sense to have the highest quality of evidence for any treatment. Balancing these demands should be straightforward. It means providing early access to treatments, but ensuring that we gather the data at the same time.

鈥淭he most important message is that we, as a society, need to keep pushing for large, well-designed research studies and keep on reassessing,鈥� says Gerstein. 鈥淚f we鈥檙e treating people the same way we did 30 years ago, then we鈥檙e probably not treating them right.鈥�

Efforts are underway to ensure that this happens. Medical specialty organisations, like the American College of Physicians, have an 鈥� and reassess them as new studies are published. Jones says that many medical conferences now insist on some form of peer review before new practices can be presented. And as part of its safety surveillance programme, the FDA has a comprehensive for drugs and devices.

In addition, researchers are trying to change the culture surrounding clinical trials to . at Stanford University is leading the push for medical journals to set more rigorous standards for the publication of results 鈥� and to have external groups monitor those standards. The aim is to highlight potential funding biases and stop flawed results from sneaking their way into everyday medicine.

There are also attempts to address the problem further upstream. It used to be that medical education was predominately an exercise in memorisation. But now teaching critical thinking has become central to the curriculum for doctors and other health professionals and there is a much greater focus on the need for evidence-based practice.

鈥淚f we鈥檙e treating people the same way we did 30 years ago, then we鈥檙e probably not treating them right鈥�

鈥淚 give a lecture to the medical students every year where I tell them the most important thing they need to know is that, one day, they鈥檒l learn everything they learned in medical school is wrong. Some of it may even be considered malpractice,鈥� says Gerstein. 鈥淲hat we currently believe today based on the evidence will change 鈥� so every doctor, as much as possible, has to keep up to date with new research because things can and do change all the time.鈥�

It may be too much to ask for our doctors to follow every incremental change. But they should be willing to examine the benefits and drawbacks of the therapies they are offering, says Cifu. 鈥淚t should be okay for doctors to discuss options with each patient and say, 鈥楲ook, I鈥檓 not completely convinced about this therapy because the data isn鈥檛 so good but it鈥檚 low risk and I think there鈥檚 a chance it could work for you and here鈥檚 why.鈥� That way patients understand they are taking a little bit of a chance but there are potential benefits.鈥�

Patients can spur their doctors on as well. When a therapy or surgery is suggested, instead of immediately asking about side effects or cost, Cifu wants them to start at a more fundamental level. 鈥淭he real questions are, how is this actually going to help me? Will this actually decrease my risk of having a heart attack?鈥� He wants ordinary people to be empowered to ask about the evidence and possible alternatives.

It won鈥檛 be easy, and doctors can feel intimidated when their patients push back. But, as Cifu says, 鈥淭hat鈥檚 the job of a good physician 鈥� to answer those questions.鈥�

This article appeared in print under the headline 鈥淢isguided medicine鈥�