Thiamine hydrochloride (vitamin B1) is used to prevent or treat low levels of vitamin B1 in people who do not get enough of the vitamin from their diets. Most individuals who consume a normal diet do not require extra vitamin B1. However, certain conditions, such as alcoholism, cirrhosis, and stomach or intestinal problems, can lead to low levels of vitamin B1. Vitamin B1 plays a crucial role in maintaining the health of nerves and the heart. Insufficient levels of vitamin B1 may cause heart failure and mental or nerve-related issues.