Phentermine is a stimulant that affects the central nervous system. It is commonly prescribed alongside a regimen of diet and exercise for the short-term management of obesity. By reducing appetite, Phentermine can help individuals eat less and, consequently, lose weight. It is important to note that Phentermine is generally prescribed for people with a body mass index (BMI) of 30 or greater, or for those with a BMI of 27 or greater who have weight-related health issues.