Background: Hepatic steatosis is associated with increased surgical complications in patients undergoing bariatric surgery. The aim of this study was to evaluate the effect of phentermine in reducing hepatic steatosis, adipose tissue and surgical complications in patients undergoing bariatric surgery. Methods: This study is a two-arm, double-blind, randomized, controlled pilot trial of 64 adult subjects with BMI >35 kg/m2 selected for bariatric surgery randomized to phentermine 15 mg once daily for 8 week or placebo. Both groups adhered to a hypocaloric diet and individualized exercise program. The primary end point was the reduce frequency of hepatic steatosis measured by ultrasound and the reduce adipose tissue through fat mass in total kilograms or percentage. Key secondary points were the prevalence of surgical complications. Baseline and final biochemical parameters and blood pressure too were assessments. Results: Phentermine group the frequency of hepatic steatosis decreased 19%, and the percentage of patients with a normal ultrasound increased from 9% to 20% (p= 0.053). Likewise, the decrease in fat mass in kilograms was greater in the phentermine group (56.1 kg vs. 51.8 kg, p=0.02), and a significant decrease in the HOMA-IR index was observed regardless of weight loss. No differences in surgical complications were observed between groups. Phentermine was well tolerated; no differences were observed in the frequency of adverse events between the groups. Conclusions: Phentermine decreased the proportion of individuals with hepatic steatosis by 19%, promoted a greater loss of fat mass in kilograms, and decreased insulin resistance among candidates for bariatric surgery.