Advil is a nonsteroidal anti-inflammatory drug (NSAID) used to relieve pain and reduce fever. According to the sources provided, there are several side effects that may occur when taking Advil.

The most common side effects of Advil are gastrointestinal, such as stomach pain, nausea, and heartburn [2]. These side effects may be minimized by taking the medication with food or milk [3]. However, if these symptoms persist or worsen, it is important to seek medical attention.

In rare cases, Advil can cause serious gastrointestinal problems, such as bleeding or perforation of the stomach or intestines [2]. These complications are more likely to occur in elderly patients or those with a history of stomach ulcers or bleeding [1]. Therefore, it is important to use Advil with caution and under the guidance of a healthcare professional.

Other potential side effects of Advil include headache, dizziness, and drowsiness [3]. These side effects are usually mild and temporary, but if they persist or become severe, medical attention should be sought.

Advil may also cause allergic reactions, such as hives, difficulty breathing, or swelling of the face, lips, tongue, or throat [3]. If any of these symptoms occur, medical attention should be sought immediately.

It is important to note that this is not a complete list of all possible side effects of Advil. Patients should always read the medication label and consult with a healthcare professional before taking any medication.

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