But this week, the publication of three studies in The Lancet, has added a new benefit to the equation: cancer prevention, and stirred up the pros and cons debate.
In those studies, Professor Peter Rothwell of Oxford University in the UK, a world expert on aspirin, and colleagues, confirm that for people in middle age, a daily dose of aspirin can cut the risk of developing several cancers, with effects starting after only two to three years rather than the ten or so previously thought.
Moreover, they propose that treatment with daily aspirin may also prevent an existing, localized cancer from spreading to other parts of the body, which Rothwell says is just as important to know about, since that's when cancer becomes deadly.
If you follow their reasoning, we appear to have reached a crucial point in the debate: on the one hand we have the benefit that aspirin can reduce cancer, stroke and heart attacks, which are much more likely to lead to disability or death, and on the other, we have the risk of internal bleeding, which is less harmful than those diseases.
But, although Rothwell and colleagues present compelling evidence, despite some limitations, their papers do not necessarily furnish a clear answer to that question.
Nevertheless, the balance of the pros and cons may alter in the light of their evidence, because not only does low dose aspirin therapy appear to increase the pros, it may also reduce the cons, in that the researchers found the risk of internal bleeding reduced with time.
Plus, the new studies also raise a thorny public health question, similar to that surrounding cholesterol-busters, should health authorities consider recommending routine use of aspirin for cancer prevention?
This was the subject of a commentary published in the same issue of the The Lancet. Here, Andrew T Chan and Nancy R Cook of Brigham and Women's Hospital, Harvard Medical School, Boston, suggest that on balance, we are not ready to recommend aspirin for cancer prevention.
One reason is that the Rothwell studies did not include data from the largest randomized trials in primary prevention, the Women's Health Study (WHS), and the Physicians' Health Study (PHS), where subjects took aspirin every other day.
"Also, despite a convincing case that the vascular and anticancer benefits of aspirin outweigh the harms of major extracranial bleeding, these analyses do not account for less serious adverse effects on quality of life, such as less severe bleeding," they add.
However, Chan and Cook acknowledge that as we await results of additional trials, and the longer term follow up of the WHS and PHS, the Rothwell studies do move us a "step closer to broadening recommendations for aspirin use".
At the very least, it means future evidence-based guidelines cannot ignore the use of aspirin for prevention of vascular disease in isolation from cancer prevention, they conclude.
Other authorities have also been quick to respond to the new studies. In the UK, the NHS's answer to the question "Should I start taking aspirin?" is:
"Overall, aspirin is a highly effective medical treatment when used appropriately, but it is not yet a drug that should be taken unsupervised on a daily basis, even at low doses."
They, like Chan and Cook, say that while the Rothwell studies "provide compelling evidence, taking aspirin is not yet recommended to prevent cancer and people should not start taking it daily as a precautionary measure."
For healthy people considering taking daily aspirin, they have this message:
"Given that the potential risks could outweigh any benefits, it is not currently advised that healthy people with no risk factors for cardiovascular disease take aspirin to prevent possible cardiovascular events such as heart attack and stroke."
They also say the evidence for taking aspirin purely to prevent cancer or to treat it is "even less substantial than for blood thinning", and urge "we cannot be sure that the potential benefits are not outweighed by the known risks".
The reason aspirin is prescribed in a small daily dose as a means to lower the risk of heart attack or stroke, is because of the effect it has on the clotting action of platelets in the bloodstream.
When we bleed, platelets in the blood build up at the site of the wound, forming a plug that stops further blood loss.
But this clotting can also happen inside blood vessels, such as when a fatty deposit in a narrow artery bursts. At the site of the burst, blood platelets clump into a clot that can block the artery and stop blood flow to the brain or heart, resulting in a stroke or heart attack.
Aspirin reduces the ability of the platelets to clump, thereby lowering the risk of having a heart attack or stroke.
But the downside to this anti-clotting benefit, is that aspirin can also cause serious harm, the best known of these being the small but important increased risk of stomach irritation and bleeding.
And, ironically, while daily aspirin can help prevent a clot-related (ischemic) stroke, it may actually increase the risk of a bleeding (hemorrhagic) stroke.
Although aspirin's risk-reduction benefits are different between men and women (and among women, it also depends on age), the risk of bleeding with daily aspirin is about the same in both sexes.
The risk of bleeding also tends to be higher in older people, those with a history of stomach ulcers, and people already taking medication or who have conditions that increase the risk of bleeding.
Daily aspirin use also increases the risk of developing a stomach ulcer. And, for anyone with a bleeding ulcer, taking aspirin will cause it to bleed more, perhaps to a life-threatening extent, say experts at the Mayo Clinic in the US.
People with asthma can also experience breathing problems with aspirin.
Other side effects of taking aspirin include nausea and indigestion, ringing in the ears (tinnitus) and hearing loss. And some people can have an allergic reaction.
Aspirin recommendationsBefore you take aspirin, even as a pain reliever, experts generally recommend that you talk to your doctor or pharmacist if you are pregnant, trying to conceive or are breastfeeding.
The same goes for people with a blood disorder, a stomach ulcer, who suffer from asthma, have high blood pressure, kidney or liver problems, or have allergic reactions to any drugs.
It is also important to tell your doctor what other medications or supplements you are taking. Even if you take aspirin with ibuprofen, it reduces the benefits of the aspirin. And taking aspirin with other anti-clotting agents, such as warfarin, could also greatly increase your risk of bleeding.
If you are on daily aspirin and need surgery or dental work, it is important you tell your surgeon or dentist what dose you are on, so they can minimize the risk of excessive bleeding during the procedure.
The US Food and Drug Administration (FDA) also warns those who take aspirin regularly to limit their alcohol intake, because that can have an additional blood-thinning effect, and raises the risk of upset stomach.
The Mayo Clinic suggest if you are on daily aspirin, you should limit your alcohol consumption to one drink or less per day if you are a woman, or two drink or less if you are a man.
Another point they make, is that stopping daily aspirin therapy may be unsafe: there is a rebound effect that can trigger a blood clot and cause a heart attack or stroke. It is important to talk with your doctor first before you make any changes or stop your daily dose.
Aspirin should not be given to children under 16 because of the risk of triggering a rare but dangerous condition known as Reyes syndrome, which is why in the UK it has been removed as an ingredient from all child and baby medicines.
Many experts would also advise those thinking about taking daily aspirin as a way to cut cancer risk, to consider there are many other, less harmful lifestyle changes that can also make a difference: such as giving up smoking, following a healthy diet, limiting alcohol intake, keeping to a normal weight, and taking regular exercise.
Written by Catharine Paddock PhD