How does aspirin cause stomach ulcer symptoms?

How Aspirin Irritates the Stomach Lining

Aspirin, or acetylsalicylic acid, triggers stomach ulcer symptoms mainly by disrupting the stomach's protective mucus barrier and promoting direct damage to the mucosal lining. It inhibits cyclooxygenase (COX) enzymes, particularly COX-1, which reduces prostaglandin production. Prostaglandins normally stimulate mucus and bicarbonate secretion while maintaining blood flow to the stomach lining—without them, acid and pepsin erode the tissue, leading to erosions or ulcers.[1][2]

Step-by-Step Mechanism of Damage

1. Topical Irritation: Aspirin is a weak acid (pKa 3.5) that remains mostly unionized in the stomach's low pH (1.5-3.5), allowing it to diffuse into surface epithelial cells. Inside cells, it ionizes, trapping hydrogen ions and causing local toxicity, cell death, and barrier breakdown.[3]
   
2. Prostaglandin Inhibition: Systemic absorption blocks COX-1, cutting protective secretions by 50-70% within hours of dosing. This exposes the mucosa to gastric acid.[1]
   
3. Increased Acid Effects: Reduced blood flow worsens injury, as aspirin also uncouples oxidative phosphorylation, depleting ATP and impairing repair.[2]
   
   High doses (over 2g/day) or long-term use amplify risks, with symptoms appearing in 10-20% of chronic users.[4]
   
   

Common Symptoms and Their Causes

• Pain or Burning: Erosions expose nerve endings; pain worsens on an empty stomach as acid contacts raw tissue.
  
• Nausea and Vomiting: Inflammation signals the brain via vagal nerves.
  
• Bleeding: Ulcers erode capillaries, causing occult blood loss or hematemesis in severe cases (risk 2-4% yearly in users).[4]
  
• Heartburn/Indigestion: Excess acid reflux from weakened mucosa.
  
  Symptoms often start subtly after days to weeks but can escalate quickly.
  
  

Who Gets hit Hardest and Why

Risk jumps with age over 60, prior ulcers, Helicobacter pylori infection (synergistic damage), concurrent NSAIDs/steroids, alcohol, smoking, or anticoagulants. Enteric-coated aspirin delays but doesn't prevent systemic COX inhibition.[1][3]

Prevention Tactics That Work

Take with food or antacids to buffer acid. Switch to COX-2 selective NSAIDs like celecoxib for lower risk. Proton pump inhibitors (PPIs) like omeprazole restore protection by boosting mucus and cutting acid 90%.[2][4] Misoprostol mimics prostaglandins but causes diarrhea in 20-30%.[1]

Sources
[1]: PubMed - NSAIDs and peptic ulcer disease
[2]: NEJM - Mechanism of NSAID-induced gastropathy
[3]: Gastroenterology - Aspirin mucosal injury
[4]: AGA Guidelines on NSAID Gastropathy