In my layman's opinion, it seems to be mostly theoretical but there is enough concern that an interaction between O3 and asprin needs to be considered. Both are proven to thin the blood and the affect is additive.
http://www.nlm.nih.gov/medlineplus/drug ... shoil.html
Omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids ("Eskimo" amounts) may increase the risk of hemorrhagic (bleeding) stroke. High doses have also been associated with nosebleed and blood in the urine. Fish oils appear to decrease platelet aggregation and prolong bleeding time, increase fibrinolysis (breaking down of blood clots), and may reduce von Willebrand factor. Fish oil should be used cautiously in patients with abnormal heart rhythms (ventricular tachycardia). http://www.igan.ca/id67.htm
Interaction with NSAIDs. There is one specific drug interaction that needs to be considered. Fish oil may enhance anti-platelet action of Aspirin and other NSAID's ( COX-1 type, Ibuprofen, others). Therefore, use of fish oil together with aspirin (especially daily low dose as used to prevent strokes and heart attacks) may be harmful. As with everything else you may read on this website, the decision to use fish oil or not in combination with these drugs must be taken by patient and nephrologist together, weighing potential risk and potential benefits. There cannot be a blanket recommendation that applies to everyone.