Nonsteroid anti-inflammatory drugs (NSAID) for example ibuprofen, naproxen, diclofenac, mefenamic acid etoricoxib,indomethacin,celecoxib and aspirin for pain relief (low-dose aspirin is not usually considered as an NSAID), are not recommended after Roux-en-Y gastric bypass (RYGB) because of the increased risk of marginal ulcers.

People who have had Gastric Bypass are more susceptible to ulcers specifically marginal ulcers which are ulcer that occurs at the margin of the gastric pouch and the small intestine.

Your stomach before gastric bypass leads to the duodenum which is a part of the small intestine. The duodenum is able to handle gastric acid. After Gastric Bypass the gastric pouch connects to another part of the small intestine that is called the jejunum. The jejunum is not able to handle gastric acids as much as the duodenum and is more susceptible to ulcers in this spot.