How do NSAIDs cause gastrointestinal side effects?

How do Non-Steroidal Anti-inflammatory Drugs cause gastrointestinal symptoms, ulcers and bleeding?

NSAIDs work by inhibiting an enzyme called cyclooxygenase (COX), which produces prostaglandins - substances involved in inflammation.

But COX isn't just involved in the inflammatory response, it also helps produce the bicarbonate and mucus that buffer the stomach against its own acidity.

By blocking COX, NSAIDs compromise this protective lining, damaging cells in the stomach, small intestine and large intestine. Over time, this can lead to ulceration, increased intestinal permeability and bleeding, which in turn can contribute to iron deficiency.

Examples of NSAIDs by COX selectivity:

Non-selective (COX-1 and COX-2) inhibitors:
Diclofenac (Voltaren), ibuprofen (Nurofen), naproxen (Naprogesic), aspirin, mefenamic acid (Ponstan), meloxicam (Mobic), indomethacin (Indocid), ketoprofen (Orudis)

COX-2 selective inhibitors:
Celecoxib (Celebrex)