Antidepressants such as Paxil could potentially cause stomach bleeding, especially when combined with nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, naproxen, and ketoprofen. Consult your doctor before combining Paxil with NSAIDs or blood-thinning drugs.
In clinical testing, gastritis was observed "infrequently" and I can't find a listed contraindication. Clearly, as Paxil is a prescription med, this would invovle consultation with the doctor who prescribed it, so if this is a problem for the specific patient, that should be part of the consultation. Additionally, your doctor should be consulted before one starts and ongoing course of NSAIDs or any other medication, as these are generally intended for occassional use only.