Dihydroquercetin (sold as Taxifolin) was suggested in a comment on Fisetin and praised that it worked better for the reader than other items, etc. A friend tried it, as to date, noticed a distinct improvement after just a few days — especially in not having histamine issues after a meal. It’s time to review and summarize what is known about it.
Taxifolin (3,5,7,3,4-pentahydroxy flavanone or dihydroquercetin) is a flavonoid commonly found in onion, milk thistle, French maritime pine bark and Douglas fir bark. It is also used in various commercial preparations like Legalon™, Pycnogenol®, and Venoruton®….Taxifolin (3,5,7,3,4-pentahydroxy flavanone or dihydroquercetin) is a flavonoid commonly found in onion, milk thistle, French maritime pine bark and Douglas fir bark. It is also used in various commercial preparations like Legalon™, Pycnogenol®, and Venoruton®….
Modulated NF-κB activation Suppressed the NF-κB activation, protein kinase activation by C-Fos and mitogen, and reduced the expression of osteoclast-specific genes, including Trap, Cathepsin K, Mmp-9, Nfatc1, C-Fos and Rank
Inhibited the osteoclast differentiation induced by RANKL Suppressed the NF-κB signaling pathway and inhibited the osteoclastogenesis
An insight into the health-promoting effects of taxifolin (dihydroquercetin) 
Now, for histamines we find “low concentrations of H2O2[Hydrogen Peroxide] appeared to augment … histamine release induced by anti-IgE…. Since taxifolin inhibited Hydrogen Peroxide generation but had little inhibitory effect
on histamine release indicates that H202 generation is not a prerequisite for anti-lgE-induced histamine release….By contrast, taxifolin caused a large inhibition of H202 formation but had a much smaller effect on histamine release. ” .
Reading thru several studies [most from the 1980’s], we find that it was inactive against some forms of histamine release. I suspect that it dropped off the radar of people suffering with mast cell and histamine issues because of these studies (using older methodologies)
- “There was a remarkable correspondence of inhibitory activity for each of these flavonoids against TF’A-, teleocidin-and aplysiatoxin-induced histamine release. Taxifolin was essentially inactive against each tumor promoter,” 
However we also read “Dihydroquercetin in the capacity of antioxidant may be compared or exceeds many synthetic and natural antioxidants and, in particular, known bioflavonoids (quercetin) ”
The status changed in a more recent study specific to mast cells and not generic histamine.
Taxifolin inhibited degranulation, generation of leukotriene C4 (LTC4), production of interlukin-6 (IL-6), and expression of cyclooxygenase-2 (COX-2) through blocking intracellular Ca2+ mobilization, phosphorylation of phospholipase Cγ (PLCγ) and mitogen-activated protein kinases (MAPKs), translocation of cytosolic phospholipase A2 (cPLA2) and 5-lipoxygenase (5-LO), and Akt/IKK/NF-κB pathway, in BMMC cells.Inhibitory effect of taxifolin on mast cell activation and mast cell-mediated allergic inflammatory response 
An earlier study also point to too narrow a focus with these “no effect” studies
” Dihydroquercetin (taxifolin), previously considered as inactive, showed an interesting cromoglycate-like behaviour. ”
What is this behavior??
“Cromoglicic acid — also referred to as cromolyn, cromoglycate, or cromoglicate — is traditionally described as a mast cell stabilizer, and is commonly marketed as the sodium salt sodium cromoglicate or cromolyn sodium. This drug prevents the release of inflammatory chemicals such as histamine from mast cells….The underlying mechanism of action is not fully understood; ” Wikipedia
This compound seems to act in a different way than antihistamines. It does not require a prescription. In some ways it acts like cromolyn (which some people take for other conditions “in Crohn’s disease … 60% improved clinically” ). IMHO, it is likely worth trying one bottle of it. A related suggestion is to take Catelase to reduce hydrogen peroxide (and thus lower histamine release).