['This study aims to determine the influence of Roux-en-Y gastric bypass (RYGB) on medication-related costs.', 'The study analyzed the types, dosages, and costs of drugs and medical devices prescribed before and after surgery (1, 3, 6, and 12 months and yearly thereafter) in patients who underwent RYGB between June 2004 and May 2010 and had an outpatient visit between December 2009 and May 2010 at Pitié-Salpêtrière University Hospital, Paris, France.', 'The cohort included 143 patients (78 % female; mean age, 42.9 years; mean BMI, 48.6 kg/m(2)). Total prescription costs were significantly lower (-32 %, p < 0.001) 1 year after RYGB compared with preoperative costs. However, the cost for medications to prevent RYGB side effects (in particular nutritional deficiencies) displayed a 36-fold increase in the first month postsurgery, but then decreased progressively over time. Importantly, the cost related to the treatment of the two most frequent obesity-related diseases significantly decreased 1 year after surgery. Indeed, prescription costs for treatment of type 2 diabetes (T2D) and obstructive sleep apnea (OSA) (namely CPAP therapy considered as the gold standard treatment) were reduced 1 year after surgery by 85 and by 63 % (both p < 0.001), respectively. We also observed a trend toward a decrease in the prescription costs of other obesity-related diseases, although it did not reach significance in our cohort.'] Is medication cost significantly reduced after Roux-en-Y gastric bypass in obese patients?