Final answer:
Adverse reactions to celecoxib (Celebrex) can include gastrointestinal bleeding; it is a COX-2 selective inhibitor linked to serious side effects like heart attack, blood clots, and certain cancers.
Step-by-step explanation:
An adverse reaction to celecoxib (Celebrex) includes gastrointestinal bleeding among other potential reactions. Celecoxib is a COX-2 selective inhibitor, which is designed to block the COX-2 enzyme more than the COX-1 enzyme. This drug is associated with a variety of negative side effects such as increased risk of stroke or heart attack, blood clots, various forms of cancer (including breast, ovarian, colon, and endometrial cancer), gall bladder disease, and possibly psychiatric and neurologic conditions such as depression or dementia. While COX-2 inhibitors like Celebrex were believed to carry a lower risk of stomach problems compared to older NSAIDs, they still pose a significant risk for gastrointestinal issues, including gastrointestinal bleeding.