Summary: The active biological form of vitamin B1 is thiamine pyrophosphate, the cofactor of enzymatic reactions controlling energy processes, participating in the metabolism of amino acids and organic compound transformation. It is also involved in nerve signal transmission in the synapses and signaling pathways associated with the reception of stimuli from the environment. Demand for vitamin B1 varies and depends on gender, age, weight, lifestyle and state of health. The typical symptoms of thiamine deficiency are tiredness, irritability, depressed mood, difficulty in concentration. In oral therapy it is recommended to take 25–30 mg of thiamine per day. In alcoholics, higher doses, up to 100 mg/d should be given, and in therapy of pain syndromes the doses should be increased up to 2 g per day. Complementary therapy with benfotiamine is convenient and efficient in vitamin B1 deficiency. In contrast to thiamine, benfotiamine is insoluble in water, but very well soluble in fats. Thanks to this it is 3.5 times better absorbed from the gastrointestinal tract, shows higher bioavailability and 2-3 times higher concentration in the serum.