Phentermine, in doses clinically used, works on the hypothalamus portion of the brain to release norepinephrine, a neurotransmitter or chemical messenger that signals a fight-or-flight response, reducing hunger. Phentermine works outside the brain as well to release epinephrine or adrenaline causing fat cells to break down stored fat, but the principal basis of efficacy is hunger-reduction. At high doses, phentermine releases serotonin and dopamine as well, but such doses are never used in clinical medicine.[2]

Dosing and administration

Generally, it is recommended by the Food and Drug Administration(FDA) that phentermine should be used short-term (usually interpreted as 'up to 12 weeks'), while following nonpharmacological approaches to weight loss such as healthy dieting and exercise.