Does the drug vincristine cause blood clots in the bowel, grandad had rcvp them had a blood clot in the major artery supplying the bowel?

I suspect this was..: True...True and unrelated. Coagulopathy, is not a side effect of vincristine. However, having a cancer (such as lymphoma that i suspect your dad has) can elevate clotting risk all by itself. Prednisone in rcvp can elevate risk of clotting as well. Additionally, as a 67yo man, he could have had pre-existing vascular disease that elevated his risk for clotting in those vessels that supply the gut.