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How can aspirin and other NSAIDs cause stomach erosions and ulcers?

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Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) cause stomach erosions and ulcers primarily by inhibiting the synthesis of prostaglandins.123

Under normal conditions, prostaglandins play a vital protective role in the gastrointestinal tract. They stimulate the secretion of mucus and bicarbonate, which form a protective barrier that shields the stomach lining from the corrosive effects of gastric acid and digestive enzymes. Prostaglandins also promote the repair and replacement of the mucosal lining.453

By inhibiting the enzymes (specifically cyclooxygenase) responsible for producing these prostaglandins, NSAIDs weaken the stomach's natural defenses. When this mucosal barrier is compromised, the lining becomes vulnerable to the acidic environment of the stomach, leading to the development of erosions—lesions confined to the superficial layers—or peptic ulcers, which extend into deeper tissues. Prolonged use or high doses of these medications significantly increase the risk of such gastrointestinal damage.2316