Vitamin B! also known as thiamine
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So far, no research studies have proven that an over-the-counter medication can treat Parkinson's, but people are understandably eager to try something that might. Always talk with your personal physician before adding any supplement to your regimen.

Here we discuss what we know about one supplement that has been the subject of recent attention in the Parkinson's community. Early work on thiamine, also known as vitamin B1, suggests a theoretical benefit in PD, but definitive evidence is lacking.

What is thiamine?
Thiamine helps cells use glucose for energy. Many foods, such as enriched whole grains, meats, nuts and beans, as well as over-the-counter dietary supplements contain thiamine.

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https://www.michaeljfox.org/news/thiamine-vitam...

Thiamine (Vitamin B1) and Parkinson's

https://www.michaeljfox.org/news/thiamine-vitamin-b1-and-parkinsons

Never heard of this would like to know myself.