Bariatric surgery is considered an appropriate method in cases of obesity, such as severe or comorbidities obesity. However, the number of patients requiring bariatric surgery is growing  constantly and rapidly. Opposing that, the anatomical modifications of the gastrointestinal tract often lead to a significant alteration in the pharmacokinetics of orally administered drugs in terms of absorption of drugs and the bioavailability of oral medications required after the surgery. The current study investigates the correlation between reduced body mass following bariatric surgery and the bioavailability of orally administered drugs. Therefore, it is required to warrant through clinical studies that help establish guidelines related to common oral drugs prescribed and monitor the medications that exhibit a small therapeutic window that should be assessed, excluding the clinical endpoint. Furthermore, the use of pharmacokinetic modeling based on a mechanical method to simulate the multivariate nature observed while changes occur during the exposure of drugs will help to serve as an essential tool to understand further the trends in oral exposure of drugs in postoperative cases develop practical clinical guidance.