Prescription Medications to Treat Overweight & Obesity. What are overweight and obesity? Health care professionals use the Body Mass Index (BMI), a measure of your weight in relation to your height, to define overweight and obesity. People who have a BMI between 25 and 30 are considered to be overweight. Obesity is defined as having a BMI of 30 or greater. You can calculate your BMI to learn if you are overweight , have obesity , or have severe obesity, which may increase your risk of health problems. Your health care professional can assess your individual risk caused by your weight. If you are struggling with your weight, a healthy eating plan and regular physical activity may help you lose weight and keep it off over the long term. If these lifestyle changes are not enough to help you lose weight or maintain your weight loss, your health care professional may prescribe medications as part of your weight-control program. How common are overweight and obesity? Obesity is a