what is phentermine?

Phentermine is an appetite suppressant (FDA approved) to help reduce weight in obese patients when used short-term and combined with exercise, diet, and behavioral modification. Like many other prescription drugs, it works with neurotransmitters in the brain. Phentermine is a centrally-acting stimulant chemical, and stimulates neuron bundles to release a particular group of neurotransmitters known as catecholamines. The neurotransmitters signal a fight-or-flight response in the body which, in turn, puts a halt to the hunger signal. As a result, it causes a loss in appetite because the brain does not receive the hunger message. Thus, you lose weight! Whoopee! =) Phentermine is typically prescribed for individuals who are at increased medical risk because of their weight but is now prevalent among dieters.
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Info Source: Wikipedia