If you don't take the correct form of B1 you will have uric acid issues and potentially kidney stones. The proper form for PD is HCL NOT B1 mononitrate. Most forms of B1 are of the kind mononitrate, so read your label.
When taking high doses of B1 it is suggested that after a time you would also need to add in other nutrients such as magnesium and potassium and the other B vitamins.
A moderate dose of magnesium, as per Dr. Constantini, is 375mg extended release 2x a week, but only after the proper amount of B1 has been established, the proper amount being that which, hopefully, alleviates symptoms. This amount is apparently different for each person, each person being different after all. B1 in pill form needs to be in high doses, I read, because the B1 pill goes thru the digestive system. B1 administered in injections or taken sublingually does not, they say, go thru digestion and so lower doses are appropriate. All this information is from my research.

We are currently in the process of establishing our baseline of B1. My husband is on currently on 300mg of HCL/day (for about a month) with some small but real relief. We are looking forward to upping this dosage by 100mg shortly. We are going slowly and conservatively to avoid any adverse reactions. So far so good. I myself am taking B1 maybe every other day just to increase my energy levels and I can say I do feel more energetic and upbeat. Since I have kidney stones, I need to add in magnesium.
Well, this sums up all I know about B1. If anyone has good luck with it, sing out.

I’m taking Thiamine HCI And successfully reversing symptoms. I started with 1000 mg a day. And a week later went to 2000 mg. It’s been extremely successful in Reducing symptoms, Over the last 14 weeks.Dr. Constantini says high doses are necessary for reduction of symptoms. Many people with Parkinson’s are using this therapy. I see my story page on this site.

I am taking Tart cherry extract for the build up of Utica acid!!

See my story page

My Hubby is now on 900mg or 9 X 100mg tablets per day. Hez very happy with his improvement.