Thiamin Mononitrate (Vitamin B1), Microcrystalline Cellulose, Dicalcium Phosphate, Magnesium Stearate. Thiamine (also known as Vitamin B1) is a water soluble vitamin of the B Complex. It has several important functions, including working with other B-group vitamins to help break down and release energy from food, as well as keeping nerves and muscle tissue healthy.