How long does it take for the clotting effects to wear off. Assuming one dose of around 600mg of aspirin and exactly how much effect does it have on clotting of minor bleeds?

1 Answer 1


According to Tulane's pharmwiki, the half-life of aspirin for a dose of 300-650 mg is 3.1-3.2 hours. The half life of a drug is the amount of time needed for the concentration of drug to be reduced in half (after reaching peak concentration).

So, after 5 half-lives, or roughly 16 hours, the amount of drug remaining in the body is (1/2)^5 = 0.03125 -> 3%, which is mostly eliminated from the body.

*I only use 5 half-lives because it was a rule of thumb for drug elimintion mentioned in the Youtube video in my references. A more conservative answer could be 6 half-lives (1.5625% drug remaining in blood) or rougly 19 hours.


In this image, 1 hour is the half life.

Aspirin functions as a blood thinner by irreversibly inactivating a protein called the COX enzyme in platelets, which disrupts the clotting process. This is why a possible serious side effect of taking aspirin is bleeding a lot from a minor cut.

In summary, in those 16 hours in which the aspirin is in action, the platelets (life span: 8-9 days) that are affected will be unable to clump together to clot which can pose a risk for minor bleeds.


Pharmacological Information on Aspirin

Quick Youtube Video with half-life example problems

Educational Resource on Safe Usage of Aspirin

Biochemical Action of Aspirin and Cost-Benefit Analysis

Image Source

  • 2
    Good answer except you focus on half-life, which gives the misleading impression that 5-6 half lives is the answer to the OP's question. You only mention the prolonged effect on platelets at the very end, and seemingly almost as an afterthought. I think your last paragraph is the real answer and should be emphasized over half-life.
    – Carey Gregory
    Mar 29, 2018 at 17:14
  • This does answer my question at the end :) One reason I asked was that I had a blood test and it bled a lot afterwards and they asked if I'd had aspirin and I said "no" but then said, well yes, but two days ago and they said that would be it then. I was a little skeptical but it sounds like they were correct. It's put me off taking aspirin to be honest if it has that much effect on my clotting several days later...
    – jcoder
    Apr 3, 2018 at 10:30

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