Earlier this month, the U.S. Food and Drug Administration rejected a decade-old request from Bayer HealthCare LLC, the maker of Aspirin, to label the popular drug as an effective way of preventing heart attacks and strokes.
This comes as a bit of a surprise because, since the late 1980s, cardiologists and family doctors have been recommending that many patients take Aspirin every day as a way to prevent cardiovascular events.
In fact, doctors routinely recommend that people over 50, as well as people with diabetes, take a baby Aspirin (81 mg as opposed to 325 mg for a regular Aspirin) daily to ward off heart problems. There is also some research that suggests routine Aspirin therapy can prevent colon cancer and breast cancer, even though the evidence for all these claims is fairly scant.
(A small technical aside: In Canada, Aspirin is a brand name and its active ingredient, acetylsalicylic acid (ASA), is also sold in generic form. In the United States, Aspirin is also sold by Bayer but aspirin is a generic term for ASA.)
The FDA – which is infinitely more consumer-friendly than its counterpart Health Canada – issued a clear and factual "consumer update" to explain its rationale. "Can an aspirin a day help you ward off a heart attack or stroke?" the FDA missive begins. "That depends. Scientific evidence shows that taking an aspirin daily can help prevent a heart attack or stroke in some people, but not in everyone. It also can cause unwanted side effects."
What is indisputable is that taking ASA daily can significantly reduce the risk (by about 25 per cent) of another heart attack or stroke in people who have already suffered significant cardiovascular problems.
What is a lot less clear, and the subject of heated debate for decades, is whether taking Aspirin can prevent a heart attack or stroke in relatively healthy people (read: no history of heart disease).
ASA reduces clotting – and clots that block circulation are what cause most heart attacks and strokes – so prescribing daily Aspirin seems like a sensible thing to do, at least on the surface. The problem is that ASA has side effects, notably causing gastrointestinal bleeding. It can be particularly dangerous for people taking other blood-thinning drugs.
When you take any drug, it is essential to weigh benefits against risks.
According to an analysis of nine large clinical trials of Aspirin for primary prevention that was published in the Archives of Internal Medicine in 2012, the benefits are modest and the risks not insignificant. Specifically, the researchers found that for every 120 people who take ASA daily, one cardiac event will be prevented. At the same time, a "non-trivial bleeding event" will occur in one in every 73 people.
Put another way, almost twice as many people will be harmed as will benefit from a regime of daily Aspirin. And, just as importantly, there is no effect on mortality.
While the FDA would not allow Aspirin to be labelled as a drug that prevents heart attacks and strokes, it's worth noting that it said that the decision to use the therapy ultimately rests with individual physicians and their patients.
It also needs to be said that Canadian and American guidelines differ fairly significantly on the issue of ASA/Aspirin for prevention.
Groups like the American Heart Association recommend daily Aspirin for anyone with moderate risk factors for heart disease, even if they have not had a heart attack or stroke. Those risk factors include smoking, obesity, high blood pressure, high cholesterol or diabetes.
The guidelines from the Canadian Cardiovascular Society are more cautious. They say, essentially, that routine prescription of daily ASA is not recommended but can be appropriate for certain patients.
The reality though is that, in the Internet age, many people self-medicate. It is estimated that some 40 million Americans and four million Canadians take daily Aspirin, despite the weak evidence that it will benefit most of them.
The real tragedy is that too few people who can definitely benefit from daily ASA therapy – survivors of heart attacks and strokes – are taking the drug, and too many people for whom daily Aspirin is of dubious value have embraced it.
Aspirin has been around for a long time – since 1897 as a commercial product, and its root chemical salicylic acid, found in willow bark, has been used since the time of Hippocrates. In cyberspace, there is much hype about Aspirin and related drugs, and the cautions about the risks and limitations are a lot more difficult to find. It's a cheap, relatively safe drug and that's attractive, but the potential harms can't simply be ignored.
We have to be careful to not overreach.
What the research tells us is that Aspirin/ASA is effective for treating the occasional headache, but is not particularly effective at preventing heart disease.
Though the evidence is not what we really want to hear, it's still the best guidance we have.