As you probably know, low dose (up to 75mg per day typically) aspirin is given to people with a cardiovascular 'history' so as to lower the risk of heart attack or stroke (because aspirin thins the blood, and reduces the risk of clots).
What is gradually becoming clearer is that up to 25% of people given aspirin are resistant to its blood thinning effects. This is likely due to a combination of genetics and the processes involved in insulin resistance. Worse, those people who are resistant to aspirin in this way are probably at higher risk of clot build up than those who are not resistant!
This is a major issue. Luckily, it seems that a test has been developed which can screen for those with resistance and we can expect this to be deployed over the next few years.
It might mean that for those with high risk factors, and who are resistant to aspirin, other more intensive medications might be required. Or, that if you find out you are one of these people, that you have an more urgent reason to reduce these risk factors yourself.
(Footnote: daily low-dose aspirin may confer other benefits for those over 50 years of age - in particular cancer risk reduction - see this article).