Advil is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain, fever, and inflammation. According to the sources provided, stomach issues are a possible side effect of Advil. MedlinePlus [2] notes that taking Advil can increase the risk of stomach bleeding and ulcers, especially in people who are older, have a history of stomach problems, or take other medications that can increase the risk of stomach bleeding. GoodRx [3] lists stomach pain, nausea, and vomiting as common side effects of Advil. Additionally, Drug Patent Watch [1] mentions that Advil can cause gastrointestinal disturbances, including abdominal pain, dyspepsia, and diarrhea.

It is important to note that not everyone who takes Advil will experience these side effects. However, if you do experience stomach issues while taking Advil, it is important to talk to your doctor. They may recommend taking a lower dose or switching to a different medication. In some cases, they may also recommend taking Advil with food to help reduce the risk of stomach problems.

In conclusion, stomach issues are a possible side effect of Advil, as noted by MedlinePlus, GoodRx, and Drug Patent Watch. It is important to talk to your doctor if you experience any side effects while taking Advil.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ADVIL
[2] https://medlineplus.gov/druginfo/meds/a682159.html
[3] https://www.goodrx.com/advil/advil-side-effects