Millions take aspirin to prevent heart disease and cancer. Turns out that’s risky.

An aspirin a day has long been been touted as one of the pillars of a healthy routine for older people: Swallow the pill and see your risks of heart disease and cancer melt away.

But the findings of a large, randomized controlled trial has just been published in three papers in the New England Journal of Medicine. Together, they show a baby aspirin a day in people 65 years and older actually increased the risk of death — mainly from cancer — and that the pill does not drive down rates of heart disease, disability, or dementia.

The trial, led by John McNeil of Australia’s Monash University, involved more than 19,000 people, mostly age 70 and older, in Australia and the US. The participants were divided into two groups: Half took a low-dose or “baby” aspirin (100 milligrams) per day, and the other half took a placebo.

Following the participants for an average of five years, the researchers compared how well the two groups fared when it came to cardiovascular disease, hemorrhages, cancer, dementia, disability, and overall mortality. The results were striking: “If you are healthy, there seems little to gain — and a fair amount to lose” from taking aspirin, as Yale cardiologist Harlan Krumholz summed up.

Aspirin takers were more likely to experience a major bleed (3.8 percent in the aspirin group versus 2.7 percent in the placebo group). They were more likely to die from cancer (3.1 percent on aspirin compared to 2.3 on placebo). They also had a higher overall rate of death (5.9 percent on aspirin versus 5.2 percent on placebo). For heart disease, disability, and dementia, taking aspirin didn’t reduce people’s risk, though it didn’t seem to increase it, either.

The researchers couldn’t explain the cancer finding and noted that previous studies contradicted it. But overall, they saw no benefits to taking aspirin, and lots of potential risks. As McNeil said in an interview with the Times, the study comes as “the ugly facts which slay a beautiful theory” about the preventive power of daily aspirin.

A few caveats about the findings: The study was concerned with aspirin’s role in “primary prevention” — whether the drug could improve health outcomes in older people who are already healthy. So the results don’t change the fact that aspirin still appears to be helpful for “secondary prevention,” or staving off illness in people who already have heart disease or stroke. It also involved older folks — most were 70 and above — so the findings don’t apply to all age groups. And more research is needed to understand the cancer findings.

The US Preventive Services Task Force recommends people ages 50 to 59, at risk of cardiovascular disease, consider a daily aspirin. They also say people ages 60 to 69 have less to gain, since the risk of bleeds in this group is higher. (Because aspirin prevents blood clot formation, which causes heart attacks and some types of stroke, it can also increase the risk of bleeding.) And the task force says people 70 and older should proceed with caution because of a lack of evidence.

This study might end up changing that guidance, Eric Topol, a cardiologist and geneticist at Scripps Research, told Vox. “We should stop giving aspirin to healthy people for primary prevention.” He added: “It’s very hard to take healthy people and make them healthier. If it isn’t broken, don’t fix it.”