Amfepramone, also known as diethylpropion, is an anorectic drug used for the short-term treatment of obesity; however, its efficacy and safety during periods greater than 3 months has been scarcely studied. To evaluate the 6-month efficacy and safety of amfepramone treatment in obese adult Mexican patients resistant to diet and exercise, a double-blinded, randomized, and placebo-controlled clinical trial study was designed on 156 volunteers with a body mass index (BMI) greater than 30 kg/m2 and less than 45 kg/m2. Patients were randomized to receive a 75 mg tablet of amfepramone or placebo daily for 6 months. Primary outcome was the absolute body weight loss, whereas secondary outcomes were the percentage of patients who achieved at least 5% or 10% weight loss, as well as the improvement of anthropometric and metabolic parameters. Amfepramone treatment produced a superior efficacy to decrease body weight than placebo at 3 months (-4.9±0.25 kg vs. -0.7±0.32 kg) and 6 months (-7.7±0.52 kg vs. -1.1±0.7 kg). In addition, 64 and 34 patients achieved at least 5% or 10% weight loss, respectively, with amfepramone at 6 months, compared with 8 and 0 patients on placebo. Amfepramone also significantly improved BMI and waist circumference, but it only showed a favorable tendency in the waist-hip index (WHI), glucose, total cholesterol, low-density lipoproteins (LDL), high-density lipoproteins (HDL), triglycerides, heart rate, systolic blood pressure, and diastolic blood pressure at 3 and 6 months. Amfepramone produced only mild adverse events, and they were presented in a greater number than placebo only at 3 months, dry mouth being the the main adverse event. Data suggest that amfepramone is effective and well tolerated in obese Mexican patients during a 6-month regimen.