Vitamin B1 (Thiamine) is a water-soluble essential vitamin that functions as a coenzyme in the form of thiamine pyrophosphate (TPP), playing an irreplaceable role in carbohydrate metabolism — particularly in the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes of the citric acid cycle. Thiamine deficiency rapidly impairs energy metabolism in high-demand tissues, particularly the nervous system and heart. Research at pharmacological doses has examined thiamine’s role in neuroprotection, metabolic disease, and mitochondrial function support, with interest in its use as an adjunct in metabolic and neurological research protocols.