Advil is a brand name for the drug ibuprofen, which is a nonsteroidal anti-inflammatory drug (NSAID) used to relieve pain, fever, and inflammation. The active ingredient in Advil is ibuprofen, which is also found in generic versions of the drug. According to the Drug Patent Watch [1], the patent for Advil expired in 2002, which allowed other companies to produce generic versions of the drug.

The Guardian [2] reports that generic drugs are required to have the same active ingredient, strength, and dosage form as their brand-name counterparts. However, the inactive ingredients may differ between the brand-name and generic versions of a drug, which can affect how the drug is absorbed and metabolized in the body. This can lead to differences in effectiveness, side effects, and safety between brand-name and generic drugs.

The Atlantic [3] notes that the FDA requires generic drugs to be bioequivalent to their brand-name counterparts, meaning that they must have the same rate and extent of absorption in the body. However, the FDA allows for a certain degree of variability in the bioequivalence of generic drugs, which can lead to differences in effectiveness between brand-name and generic drugs.

In summary, both Advil and its generic versions contain the same active ingredient, ibuprofen. However, the inactive ingredients may differ between the brand-name and generic versions of the drug, which can affect how the drug is absorbed and metabolized in the body. While generic drugs are required to be bioequivalent to their brand-name counterparts, there may be some variability in their effectiveness. It is recommended to consult with a healthcare provider to determine the best treatment option for an individual's specific needs.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ADVIL
[2] https://www.theguardian.com/science/2016/oct/03/do-branded-painkillers-work-better-than-cheaper-generic-ones-iboprofen-nurofen
[3] https://www.theatlantic.com/health/archive/2015/03/generic-drugs-the-same-but-not/388592/