A trial with 3 to 8g perday orally had little effect on Alz:
I would be wary of high doses as it shows none-specific binding to several proteins
implicated in soem PDs: eg DJ-1
The Costantini study lasted just two months and the effect of the injections was detected after 1 month. To me that suggests thiamine is increasing the acute effect of L-DOPA… So it is possible it adds to the oxidative stress of DOPA and so might speed up loss of the remaining live neurones. I dont see any evidence for neuroprotection.
However thiamine is esseantial for brain glucose metabolism and its uptake may be impaired in the elderly at gut, bbb and into oxidatively stressed neurones. Perhaps it is worth trying as an enhanced supplement over the 1.5mg pd in mutivitlamin pill. I doubt it will have much effect on neuroprotection its own, but as part of a cocktail of endogenous metabolites it might improve mitochondria .The Wahls Protocol uses such a cocktail, mine is similar.
More reading needed before I decide about adding a modest amount of thiamine to mine cocktail…