Hydrochloric acid is found naturally in the gastric juices in the stomach, where it is needed to convert the enzyme pepsinogen into pepsin, an active enzyme that breaks down proteins for further digestion in the small intestine. Hydrochloric acid is available as a dietary supplement in the form of betaine hydrochloride, which is a hydrochloric salt of betaine, a natural compound first isolated from sugar beets, but now known to be present in many plants and animals.
Betaine hydrochloride supplements should only be taken under a doctor's supervision by people with diagnosed hypochlorhydria. Prescribed doses are typically taken with or immediately following protein-containing meals. Self medicating with betaine hydrochloride is strongly discouraged, as excessive hydrochloric acid can damage the stomach lining.