Advil is a brand name for the drug ibuprofen [1]. Ibuprofen belongs to a class of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs) that are used to relieve pain, inflammation, and fever. However, NSAIDs can cause gastrointestinal (GI) side effects, including stomach ulcers [2].

Stomach ulcers are open sores that develop on the lining of the stomach or small intestine. They can be caused by various factors, including the use of NSAIDs like ibuprofen [3]. Ibuprofen works by inhibiting the production of prostaglandins, which are responsible for inflammation and pain. However, prostaglandins also play a protective role in the stomach lining by promoting the secretion of mucus and bicarbonate, which help to neutralize stomach acid. When ibuprofen inhibits prostaglandin production, it can lead to a decrease in the protective factors and an increase in stomach acid, which can cause damage to the stomach lining and lead to ulcers [2].

According to GoodRx, ibuprofen can cause stomach ulcers, especially if taken in high doses or for a long time [2]. The risk of stomach ulcers is higher in people who are older, have a history of ulcers, smoke, or drink alcohol [3]. In addition, taking ibuprofen with other NSAIDs or certain medications like corticosteroids, anticoagulants, or selective serotonin reuptake inhibitors (SSRIs) can increase the risk of stomach ulcers [2].

In conclusion, Advil (ibuprofen) can cause stomach ulcers, especially if taken in high doses or for a long time. The risk of stomach ulcers is higher in certain populations and can be increased by taking ibuprofen with other medications. If you experience symptoms of a stomach ulcer, such as abdominal pain, nausea, vomiting, or black stools, you should seek medical attention immediately [2][3].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ADVIL
[2] https://www.goodrx.com/ibuprofen/ibuprofen-stomach-ulcers-advil-motrin
[3] https://www.ncbi.nlm.nih.gov/books/NBK310269/