Described are pharmaceutical compositions comprising phentermine, metformin, and at least one pharmaceutically acceptable carrier or excipient. Another aspect of the present invention relates to a method of treating a patient suffering from obesity or needing to lose weight, comprising the step of co-administering to said patient a therapeutically effective amount of phentermine and metformin. In certain embodiments, an aforementioned method is practiced in conjunction or tandem with a medical procedure or the use of a medical device or both.