Cox-1 inhibitor: An agent that inhibits the action of the enzyme cox-1(cyclooxygenase-1). The common anti-inflammatory drugs such as aspirin,ibuprofen, and naproxen block the action of both cox-1 and cox-2. Cox-1 inhibitors can reduce inflammation, but they may also decrease the natural protective mucus lining of the stomach. Therefore, these medications can cause stomach upset, intestinal bleeding, and ulcers. In some cases, using a buffered form of a cox-1 inhibitor can eliminate or reduce these adverse effects.