The purpose of this review is to evaluate the influence of bariatric surgery on the use and pharmacokinetics of some frequently used drugs. A PubMed literature search was conducted. Literature was included on influence of bariatric surgery on pharmacoepidemiology and pharmacokinetics. Drug classes to be searched for were antidepressants, antidiabetics, statins, antihypertensive agents, corticosteroids, oral contraceptives, and thyroid drugs. A reduction in the use of medication by patients after bariatric surgery has been reported for various drug classes. Very few studies have been published on the influence of bariatric surgery on the pharmacokinetics of drugs. After bariatric surgery, theoretically, reduced drug absorption may occur. Correct dosing and choosing the right dosage form for drugs used by patients after bariatric surgery are necessary for optimal pharmacotherapy. Therefore, more clinical studies are needed on the influence of bariatric surgery on the pharmacokinetics of major drugs.