Autoimmune gastritis (AIG) is a chronic autoimmune disorder characterized by parietal cell destruction and oxyntic mucosal atrophy, leading to achlorhydria and intrinsic factor deficiency. These pathological changes impair iron and vitamin B12 absorption, resulting in iron-deficiency anemia, pernicious anemia, and neuropsychiatric manifestations. Notably, 4-12% of AIG patients develop type 1 gastric neuroendocrine tumors, while facing a 3-7 fold increased risk of gastric adenocarcinoma with an incidence of 0.9-9%. Current management of AIG is limited to iron and vitamin B12 replacement, as no disease-modifying therapies exist. The progressive hypochlorhydria reduces pepsin activity, impairs gastric motility, and promotes small intestinal bacterial overgrowth (SIBO), causing dyspeptic symptoms and micronutrient malabsorption. Furthermore, gastric hypoacidity increases N-nitroso compound formation and triggers hypergastrinemia, elevating risks for both gastric cancer and neuroendocrine tumors. This clinical trial investigates whether betaine hydrochloride (with pepsin) supplementation can restore gastric acidity and improve clinical outcomes in AIG. We will evaluate its effects on gastrin levels, gastrointestinal symptoms, exhaled gas markers (NO, H₂S, H₂, CH₄), anemia parameters, endoscopic atrophy scores, and incidence of gastric complications (hyperplastic polyps, neuroendocrine tumors, and adenocarcinoma). The study aims to provide evidence for a potential therapeutic strategy addressing both symptoms and long-term complications of AIG.