This medication is used to treat or prevent a lack of thiamine (deficiency) when the form taken by mouth cannot be used or would not work as well as the injection. Thiamine is a B vitamin that helps your body to use carbohydrates for energy. It is also important for normal function of your heart, muscles, and nervous system. Most people get enough thiamine in their diet, but certain health conditions (e.g., alcoholism, poor nutrition, pregnancy, stomach/intestinal diseases) can cause a deficiency in thiamine. Serious thiamine deficiency can lead to nerve damage, heart failure, and mental/mood conditions (e.g., confusion, psychosis).