I have noticed a few posts mentioning high dose betahistine. These two papers suggest much higher doses than the range being discussed might be required: High-dosage betahistine dihydrochloride between 288 and 480 mg/day in patients with severe Menière's disease: a case series - PubMed Betahistine Exerts a Dose-Dependent Effect on Cochlear Stria Vascularis Blood Flow in Guinea Pigs In Vivo
Perhaps it's worth mentioning that while studies on high dose betahistine say those doses are well-tolerated, it is apparently a fact that persons with a history of peptic ulcer disease need to be careful with betahistine, and that the higher doses might be even more of a problem. I was taking 48mg three times a day, along with n-acetylcysteine at 1200mg three times a day (the latter on the advice of my ENT who was not aware of my betahistine use). I have no history of peptic ulcer disease. But that combination caused significant GI pain and other GI symptoms, requiring me to stop both medicines. 2 weeks later my GI tract is improved but not back to normal. N-acetylcysteine can apparently break down the necessary mucus layer in the stomach. Not a good combination, at least in my case.