Try a Google search. Aspirin has been discussed for the past 50-60 years.
You ask a good question.
You ask a complicated question.
To explain how aspirin works is beyond the scope of this post, however it is not a "blood thinner".
Despite the fact most all medical practicioners in the United States now recommend a "baby aspirin a day", there are arguments pro and con.
The government database pubmed provides a synopsis of the most recent studies regarding the benefits of an aspirin a day and the protocols used in the studies in regard to dose.
As per Dr. Arthur Agatston
taking daily aspirin to prevent heart attack and stroke. Recent research has shed new light on this. Indeed, mounting evidence reported in a number of leading medical journals now suggests that if you’re healthy and not at significant risk for a heart attack, you should not be taking aspirin preventively. That’s because the studies show that aspirin doesn’t reduce the risk of dying from a heart attack or stroke in healthy people. Furthermore, the potential risk of a cerebral hemorrhage, gastrointestinal bleeding, and ulcers outweighs any heart benefits the aspirin might provide.
However, if you've already had a heart attack or stroke, or if you have been found by your doctor to be at high or moderate risk for heart attack or stroke, the benefits of taking aspirin can trump the risks. That’s because aspirin acts as an anti-inflammatory and an inhibitor of blood clotting. For those at risk, aspirin is one of the drugs in our arsenal (along with statins, ACE inhibitors, and beta blockers) that can help keep a coronary event from occurring in the first place or recurring.
As far as what dosage works best in people for whom aspirin is recommended, I suggest you consult your own doctor. Based on the new research, I no longer recommend aspirin (not even 81 mg low-dose, or baby, aspirin) for any of my healthy patients, because the risk of bleeding is two to four times greater than if you aren’t taking aspirin at all. I do, however, continue to recommend 162 milligrams daily (two low-dose aspirin) to patients who already have coronary heart disease, have already had a heart attack or stroke, or who are at high or moderate risk for one and not at risk for gastrointestinal bleeding.
In addition, I now follow the recently revised American Diabetes Association guidelines for aspirin use in people with diabetes. Whereas the ADA used to recommend low-dose aspirin for every diabetic patient over the age of 40, their new guidelines suggest aspirin as a prevention strategy only in those with diabetes whose cardiovascular risk is above average. This includes men over age 50 or women over age 60 with at least one additional major risk factor. In other words, according to the ADA, younger diabetic patients without associated cardiovascular risk factors appear not to benefit from taking aspirin.
Remember, if you do take aspirin regularly, you should not drink alcohol because it can also irritate the stomach lining. In addition, because aspirin is a nonsteroidal anti-inflammatory drug (NSAID), it should not be taken with other NSAIDs, such as ibuprofen or naproxen. And because it can thin the blood, avoid taking aspirin with anti-clotting medications, such as Coumadin (warfarin) or Plavix (clopidogrel), unless advised to do so by your doctor. The bottom line here is that if you’re healthy you shouldn’t take aspirin without a cardiovascular risk assessment by your doctor. If you’re not sure about your risk of heart disease, get tested. Today there are many advanced tests (such as a heart scan for coronary calcium), beyond the basic lipid profile, that can help you and your doctor determine where you stand.