Hypopepsinia is the condition of having too little pepsin — or too little peptic activity — in the gastric juice: the stomach’s protein-digesting enzyme running below par. Since pepsin is secreted as inactive pepsinogen and activated by stomach acid, hypopepsinia usually accompanies hypochlorhydria — the twin deficiencies of atrophic gastritis, pernicious anaemia, and the ageing stomach. Protein digestion suffers first: large polypeptides pass under-digested into the intestine, with bloating and poor amino-acid availability as possible consequences. The term belongs to the fine-grained vocabulary of gastric physiology, distinguishing enzyme lack from acid lack, though in practice the two deficiencies travel together and share the same causes and management.