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Gastrointestinal

Aspirin increases the risk of upper gastrointestinal bleeding. Enteric coating on aspirin may be used in manufacturing to prevent release of aspirin into the stomach to reduce gastric harm, but enteric coating does not reduce gastrointestinal bleeding risk. Enteric-coated aspirin may not be as effective at reducing blood clot risk. Combining aspirin with other NSAIDs has been shown to further increase the risk of gastrointestinal bleeding. Using aspirin in combination with clopidogrel or warfarin also increases the risk of upper gastrointestinal bleeding.

Blockade of COX-1 by aspirin apparently results in the upregulation of COX-2 as part of a gastric defense. There is no clear evidence that simultaneous use of a COX-2 inhibitor with aspirin may increase the risk of gastrointestinal injury.

" Buffering " is an additional method used with the intent to mitigate gastrointestinal bleeding, such as by preventing aspirin from concentrating in the walls of the stomach, although the benefits of buffered aspirin are disputed. Almost any buffering agent used in antacids can be used; Bufferin, for example, uses magnesium oxide. Other preparations use calcium carbonate. Gas-forming agents in effervescent tablet and powder formulations can also double as a buffering agent, one example being sodium bicarbonate, used in Alka-Seltzer.

Taking vitamin C with aspirin has been investigated as a method of protecting the stomach lining. In trials vitamin C-releasing aspirin (ASA-VitC) or a buffered aspirin formulation containing vitamin C was found to cause less stomach damage than aspirin alone.