Aspirin is a bad bargain for healthy women trying to stave off heart attacks or strokes, although it's commonly used for that purpose, according to Dutch researchers.
In a new report, they say 50 women will need to take the medication for 10 years for just one to be helped -- and that's assuming they are at high risk to begin with.
"There are very few women who actually benefit," said Dr. Jannick Dorresteijn of University Medical Center Utrecht in The Netherlands. "If you don't want to treat 49 patients for nothing to benefit one, you shouldn't treat anyone with aspirin."
The new study adds to a long-standing controversy over aspirin, one of the world's most widely used drugs.
Doctors agree it's worth taking for people who've already had a heart attack or a stroke, but they are less certain when it comes to so-called primary prevention.
"We all appreciate that the average treatment effect is very small, but that some patients may benefit more than others," Dorresteijn told Reuters Health.
Today, leading medical groups like the American Heart Association recommend aspirin for people at increased risk for heart problems.
But the Dutch findings, published in the European Heart Journal, suggest many women would still be taking the drug needlessly.
Dorresteijn and his colleagues analyzed data on nearly 28,000 healthy women age 45 and above who had received either aspirin or dummy pills in an earlier US trial.
The women on aspirin generally took a low dose of 100 milligrams every other day.
Overall, aspirin cut the rate of heart attacks, strokes and death from heart disease from 2.4 per cent to 2.2 per cent.
"Nine out of 10 women experience less than a one-per cent risk reduction for cardiovascular disease in the next ten years, so that is a really small treatment effect," said Dorresteijn.
He added that aspirin comes with side effects, too. For instance, it can cause bleeding ulcers and make people more likely to bruise due to its blood-thinning effects.
And although it's cheap -- at only a few dollars per month of treatment -- putting lots of healthy people on the drug would be a big expenditure in the health care budget, Dorresteijn said.
After subtracting the serious side effects from the health gains, the Dutch team found doctors would have to be willing to treat a lot of women to get a net advantage.
"Women older than 65 years of age benefit more than average, but still for those women the benefit was so small that you would need to treat 49 for nothing to prevent one event," said Dorresteijn. "Of course it's disappointing, because you would like a medication to be effective."
Earlier this year, two large reviews of previous aspirin trials yielded similarly sobering results. One found a tiny reduction in heart attacks with aspirin and no effect on death rates or strokes. The other showed as many as 1,111 men and women would need to take aspirin daily for the duration of the trials to prevent just one death.
The government-backed US Preventive Services Task Force advises that men age 45 to 79 take aspirin to stave off heart attacks, as long as the benefit outweighs the risk of bleeding.
For women age 55 to 79, aspirin is recommended to prevent strokes, with the same caveat.
Dr. Michael LeFevre of the USPSTF said he wasn't surprised by the Dutch findings, but added that it muddied the potential benefit on stroke by including heart attacks in the analysis.
The number of women who would need to be treated with aspirin to prevent a stroke depends on their baseline risk. If you are willing to treat only 50 women to see a net benefit for one -- that is, taking into account serious bleeds -- a woman's baseline 10-year stroke risk would have to be as high as 19 per cent.
"So if that is our threshold, almost no women will qualify," LeFevre said in an email, noting that treating 1,000 such women in their 60s will prevent 32 strokes and cause 12 bleeding ulcers.
"The central message of this study is really that there are an awful lot of women who are taking aspirin for prevention who should not be taking aspirin," he added in a telephone interview with Reuters Health. "I think the task force would agree with that."
Dr. Franz Messerli, who heads the high blood pressure program at St. Luke's-Roosevelt Hospital in New York, said there are much better ways to curb stroke risk than taking aspirin.
"First and foremost," he told Reuters Health, "make sure your blood pressure is perfectly well-controlled… because blood pressure is by far the most important risk factor for stroke."
That can be achieved by changing diet and exercise habits, or by blood pressure medications like diuretics, beta-blockers or calcium channel blockers.
People may also want to rein in their cholesterol levels, Messerli added, although cholesterol-lowering drugs themselves are controversial in primary prevention.
"The question of primary prevention has not been resolved," he said. "The good news is that that there are two ongoing randomized trials that hopefully will allow us to come to firm conclusions."