Phentermine is an appetite suppressant that was approved by the FDA in 1959 for short-term treatment of obesity. Phen- termine stimulates a group of neurotransmitters known as
catecholamines, which signal a flight-or-fight response in the body.
It is
believed that the brain does not receive the hunger signal because it is receiving the
fight-or-flight signal and focusing
on the immediate need for energy. It is also believed that
phentermine
increases the level of the hormone leptin, which signals the body to feel full.
In addition to increasing
hormones that make a person
feel full, phentermine also inhibits another neurotransmitter, neuropeptide Y. This neurotransmitter signals the body to eat,
decrease physical activity, and increase fat storage. The
combi- nation of making a person feel full, increasing
the desire to be
more physically active, and inhibiting hunger and fat storage
made phentermine seem like a great combination.
Like many of the first weight-loss drugs, phentermine is
meant for short-term use, generally no longer than six months.
Most users of phentermine can expect to see one-half to one pound of weight loss per week. One study
of
24 weeks showed that
phentermine users lost 22 pounds compared to 10 pounds of weight loss by people receiving a
placebo. During the experi- ment, all participants
were given an individualized diet, which explains
why the people taking the placebo lost weight.1 The idea is that once a person gets a “jump start” on weight loss from the drug, he or she would feel motivated to maintain the loss or ideally lose more through diet and exercise. The long-
term effects of phentermine are
unknown.
Phentermine is most
notorious for its potentially fatal interaction
with two other weight-loss
drugs, fenfluramine
(Fen-phen) and dexfenfluramine (Redux), which can cause a rare lung disorder called pulmonary hypertension as well as
heart
valve disease. When phentermine is used alone, however,
this danger appears to be absent;
for
this reason, this drug continues to be sold under the brand names Adipex-P, Fastin, Obenix, Phentercot, Pro-Fast, and Teramine. Users of phen- termine are warned by the manufacturer about this dangerous interaction with fenfluramine and dexfenfluramine.
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