Aspirin
Cyclooxygenase inhibitor / nonsteroidal anti-inflammatory drug · also known as Acetylsalicylic acid, ASA
Cyclooxygenase inhibitor that changes prostaglandin synthesis; direct MCAS evidence is a small retrospective subgroup, with important reaction and bleeding warnings.
- How it relates to mast cells
- MCAS patients
- Types of studies cited
- Case series
- Approved in the US for
- temporary relief of minor aches and pains
What this relationship means: Studied in people diagnosed with mast cell activation syndrome. Current evidence consists of case reports, uncontrolled series, or retrospective review rather than randomised comparisons — so it establishes that people have taken it, not that it worked. A 2025 practical-management review places this at step 6 of the sequence it describes — described as limited evidence, for persistent episodes despite H1 blockade. That is what the review reports, not a recommendation from this site.
Mechanism of action
Aspirin irreversibly inhibits cyclooxygenase enzymes, changing the conversion of arachidonic acid into prostaglandins. In this context it is a mediator-synthesis intervention, not a mast-cell stabiliser: it acts on a lipid pathway after mast-cell activation rather than preventing degranulation itself.
The direct MCAS source is a retrospective review of 25 patients. Aspirin exposure was reported for a nine-person subgroup selected because a urinary prostaglandin D2 metabolite was elevated. There was no untreated comparison, follow-up testing was incomplete, and the design cannot separate an aspirin effect from other changes over time.
A second retrospective report followed ten people with systemic mastocytosis. A fall in the measured prostaglandin metabolite was commonly accompanied by a substantial rise in a leukotriene metabolite. That divergence matters because blocking one arachidonic-acid branch does not mean the mediator system as a whole moved in one direction.
Safety evidence points in two directions without making an individual prediction. In a controlled aspirin-challenge study, one of 50 adults with mastocytosis reacted during the challenge; the larger retrospective cohort included histories of severe NSAID reactions. The current over-the-counter label separately warns about severe allergic reactions and stomach bleeding.
Sources
- Aspirin current US over-the-counter Drug Facts label Drug label · link checked 21 Aug 2026
- Mast cell activation syndrome: improved identification by combined determinations of serum tryptase and 24-hour urine 11β-prostaglandin2α Peer-reviewed study 2014 PMID 25439370 · link checked 21 Aug 2026
- Divergent PGD2 and leukotriene C4 metabolite excretion following aspirin therapy: Ten patients with systemic mastocytosis Peer-reviewed study 2021 PMID 34029712 · link checked 21 Aug 2026
- Low frequency of acetyl salicylic acid hypersensitivity in mastocytosis: The results of a double-blind, placebo-controlled challenge study Peer-reviewed study 2018 PMID 29569284 · link checked 21 Aug 2026