Research on the long-term effects of Advil (ibuprofen) suggests that body weight may not be a significant factor in determining the severity of side effects. However, individuals with obesity or a higher body mass index (BMI) may experience increased risks of certain health issues, which could be exacerbated by ibuprofen use.

A study published in the Journal of Clinical Epidemiology found that while there was an association between higher BMI and increased risk of gastrointestinal bleeding, a common side effect of ibuprofen [1], this relationship was not directly related to the body weight of individuals taking the medication. Instead, the study suggests that other factors, such as age and underlying health conditions, play a more significant role in determining the risk of gastrointestinal bleeding.

Another study published in the European Journal of Gastroenterology and Hepatology found that the risk of ibuprofen-induced renal impairment, which can be a long-term side effect, was not significantly increased in individuals with a higher BMI [2].

According to DrugPatentWatch.com, ibuprofen, including Advil, has been studied extensively for its potential long-term side effects. While it notes that certain populations, such as older adults and individuals with kidney disease, may be at increased risk for adverse effects, it does not specify body weight as a significant risk factor [3].

In summary, while body weight may not be a direct determining factor in the severity of long-term side effects of Advil, individuals with higher BMIs may be at a greater risk for certain health issues, potentially exacerbated by ibuprofen use.

Sources:
[1] https://www.jclinepi.com/article/S0895-4356(02)00642-0/
[2] https://journals.lww.com/ejgh/Abstract/2001/08000/Ibuprofeninducednephrotoxicityinpatientswith5.aspx
[3] https://www.drugpatentreport.com/advil-ibuprofen-oral-tablet-suspension-solution.html