Quercetin is said to have problems with absorption. As a result, it is sometimes sold combined with bromelain, which comes from pineapple, to increase absorption. Quercetin is also said to increase absorption of drugs like penicillin. However, the MOA is that (as being composed of one or more proteases), bromelain likely increases gut permeability, which seems like a bad idea for people here. Also, here's a study with heparin: "Improvement of the intestinal membrane permeability of low molecular weight heparin by complexation with stem bromelain." 2006 http://www.ncbi.nlm.nih.gov/pubmed/16950580 which gets more complicated because intestinal mast cells do contain heparin - and btw medical heparin is derived from animal intestines (and lungs).