Phentermine was first approved for the treatment of obesity in 1959, and it became very popular when articles were written about its efficacy in 1992. It was used in combination with both fenfluramine (Pondimin) and dexfenfluramine (Redux) until studies showed a possible link between fenfluramines and heart-valve problems. Today, phentermine alone is used as an appetite suppressant. It activates the adrenergic system ( i.e. the "fight or flight" response), causing it to release norepinepherine. For reasons not completely understood, this suppresses appetite. The effectiveness of phentermine has been studied in a number of trials. If we exclude those trials where it was taken with other drugs, all clinical trials have been 20 weeks or less in length. These studies show that use of this medication results in a weight loss of 6.6 pounds ( 4 kg). It is approved for short term use only, that is for a few weeks.

Although phentermine is no longer prescribed with fenfluramines, it is used in combination with other medications. Some clinicians combine it with fluoxetine (Prozac), however controlled studies are needed to show that this combination is safe and effective in the treatment of obesity. In fact, Eli Lilly, the maker of Prozac, has recommended that this drug combination should not be used at this time. Beware.

When taken alone, phentermine has some common side effects including excessively rapid heart beat, increased blood pressure, restlessness, dry mouth, constipation, and sexual dysfunction. It should not be taken with monoamine oxidase (MOA) inhibitors or within 14 days of taking these medications. Persons with advanced atherosclerosis (hardening of the arteries), symptomatic cardiovascular disease, moderately to severely elevated blood pressure, hyperthyroidism, glaucoma, severe nervousness, or a history of drug abuse should not use phentermine.