In the stomach, hydrochloric acid converts pepsinogen to pepsin, an enzyme that breaks down protein. Pepsin breaks down proteins into smaller, more easily absorbed substances. As people age, hydrochloric acid secretion may be reduced, which can result in decreased levels of pepsin. Without proper pepsin levels, the body has a difficult time digesting food. Betaine hydrochloride is used as a supplemental source of hydrochloric acid, which can be utilized by the stomach to produce pepsin. The combination of betaine hydrochloride and pepsin provide an excellent stomach tonic.