Aspirin and Rofecoxib are both non-steroidal anti-inflammatory drugs (NSAIDs) that are used to treat pain, inflammation, and fever. However, they have different effects on the stomach lining.

Aspirin is known to cause irritation and erosion of the stomach lining, which can lead to stomach ulcers and other gastrointestinal (GI) side effects. This is due to its ability to inhibit both cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) enzymes, which are involved in the production of prostaglandins that protect the stomach lining. Aspirin's effect on COX-1 is responsible for its GI side effects [1].

On the other hand, Rofecoxib is a selective COX-2 inhibitor, which means it primarily inhibits COX-2 and has minimal effects on COX-1. This selectivity reduces its impact on the stomach lining, making it less likely to cause GI side effects compared to aspirin [2]. However, Rofecoxib has been associated with an increased risk of cardiovascular events, leading to its withdrawal from the market in 2004 [3].

In summary, the key differences in stomach lining effects between aspirin and rofecoxib are:

1. Aspirin inhibits both COX-1 and COX-2, leading to stomach lining irritation and erosion, and an increased risk of GI side effects.
2. Rofecoxib is a selective COX-2 inhibitor, which reduces its impact on the stomach lining and results in fewer GI side effects. However, it has been associated with an increased risk of cardiovascular events.

Sources:

1. "Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)." American College of Gastroenterology, <https://gi.org/topics/nonsteroidal-anti-inflammatory-drugs-nsaids/>.
2. "Rofecoxib." Drugs.com, <https://www.drugs.com/rofecoxib.html>.
3. "Rofecoxib (Vioxx)." DrugPatentWatch.com, <https://drugpatentwatch.com/drugs/rofecoxib>.