Hello - thanks for asking your question.
Although I am an internal medicine physician, please see your primary
care physician for specific questions regarding any individual cases
please do not use Google Answers as a substitute for medical advice.
I will be happy to answer factual medical questions.
1) Phenteramine (also known as Adipex or Ionamin Slow Release)
Please note that Phenteramine, Adipex and Ionamin Slow Release are the
same medication. Tenuate (also known as Diethylpropion) and Bontril
(also known as Phendimetrazine) works in the same way as Phenteramine.
These medications act by stimulating the release of norepinephrine
from synaptic granules. These drugs reduce food intake either by
delaying the onset of a meal or by causing early satiety.
The efficacy of phentermine was demonstrated in a 36-week trial
conducted by Munro et. al. which found that both continuous and
intermittent administration led to more weight loss than placebo. (1)
2) Meridia (aka Sibutramine)
Meridia is a specific inhibitor of norepinephrine and serotonin
reuptake into nerve terminals. In addition to inhibiting food intake,
it also stimulates thermogenesis. In a study by Bray, there was a
clear dose response; the placebo group lost 1 percent of their initial
body weight, whereas the subjects in the 30-mg sibutramine per day
group lost 9.5 percent. (2)
In another one-year trial in which obese subjects were randomly
assigned to sibutramine or placebo after initial weight loss induced
by a very low calorie diet, the drug-treated patients lost more weight
(mean 5.2 kg) while the placebo group gained weight (mean 0.5 kg). (3)
In a trial in which 467 obese subjects who had lost weight taking
sibutramine for 6 months were then randomly assigned to receive
sibutramine or placebo for 18 months, the placebo-treated subjects
regained most of the weight they had lost, while those treated with
sibutramine regained less than 20 percent. (4)
3) Orlistat (aka Xenical)
Orlistat is currently the only drug approved in the United States that
alters fat metabolism.
Studies show weight loss at one year varied from 5.5 to 6.6 percent of
initial body weight in the placebo groups and 8.5 to 10.2 percent in
the orlistat groups. (5)
In a one-year trial, subjects were randomly assigned to placebo or one
of three doses of orlistat (90 mg, 180 mg, or 360 mg/day in three
divided doses). After initial weight loss induced by dieting, the
group assigned to the high dose of orlistat regained only 32 percent
of the lost weight as compared with regain of 56 percent in the
placebo group. (6)
I stress that this answer is not intended as and does not substitute
for medical advice - please see your personal physician for further
evaluation of your individual case.
Please use any answer clarification before rating this answer. I will
be happy to explain or expand on any issue you may have.
No internet search engine was used in this answer. All sources are
from physician-written and peer-reviewed sources.
1) Munro, JF, MacCuish, AC, Wilson, EM, Duncan, LJ. Comparison of
continuous and intermittent anorectic therapy in obesity. BMJ 1968;
2) Bray, GA, Blackburn, GL, Ferguson, JM, et al. Sibutramine produces
dose-related weight loss. Obes Res 1999; 7:189.
3) Apfelbaum, M, Vague, P, Ziegler, O, et al. Long-term maintenance of
weight loss after a very-low-calorie diet: efficacy and tolerability
of sibutramine. Am J Med 1999; 106:179.
4) James, WP, Astrup, A, Finer, N, et al. Effect of sibutramine on
weight maintenance after weight loss: a randomised trial. STORM Study
Group. Sibutramine Trial of Obesity Reduction and Maintenance. Lancet
5) Sjöstrom, L, Rissanen, A, Andersen, T, et al. Randomized
placebo-controlled trial of orlistat for weight loss and prevention of
weight regain in obese patients. European Multicentre Orlistat Study
Group. Lancet 1998; 352:167.
6) Hill, JO, Hauptman, J, Anderson, JW, et al. Orlistat, a lipase
inhibitor, for weight maintenance after conventional dieting: a 1-y
study. Am J Clin Nutr 1999; 69:1108.
7) Bray, GA. Drug therapy of obesity. UptoDate, 2003.