Thiamine is vitamin B1. Thiamine is found in foods such as cereals, whole grains, meat, nuts, beans, and peas. Thiamine is important in the breakdown of carbohydrates from foods into products needed by the body. Thiamine is used to treat or prevent vitamin B1 deficiency. Thiamine injection is used to treat beriberi, a serious condition caused by prolonged lack of vitamin B1. Thiamine taken by mouth (oral) is available without a prescription. Injectable thiamine must be given by a healthcare professional. Thiamine may also be used for purposes not listed in this medication guide.