Zantrex-3 is marketed as "the most powerful weight loss formula available without a prescription," designed to help your body more efficiently metabolize fat and burn fat.

And how does it do this. By combining not one, not two, not three but four different forms of caffeine. In addition to the caffeine listed directly, Zantrex-3 contains guarana, yerbe maté and kola nut (all of which contain forms of caffeine). In case you still haven't got it: the active ingredient in Zantrex-3 is CAFFEINE.

This combination of compounds act as central nervous system stimulants, increasing heart rate and stimulating fat and glycogen breakdown. All of these stimulants may indeed assist weight loss, but they may also lead to jitters and potential heart palpitations.

While a number of internet sites advertising Zantrex-3 boast that it has been proven effective in two clinical trials, that is not precisely the case. The actual Zantrex-3 pill has not been the subject of any clinical trials that we have been able to discover.

But unlike most supplements, three of the key compounds in Zantrex-3 -- yerbe maté, guarana and damiana (a mild laxative) -- were studied in a real (albeit small) double-blind, placebo-controlled clinical trial conducted by Danish researchers.

In this 2001 study, reported in the Journal of Human Nutrition and Dietetics, 44 healthy overweight volunteers were given either a pill containing the three compounds or a placebo three times a day before meals for a period of 10 days.  

In a parallel trial, 47 patients were given the supplement or a placebo prior to meals three times a day over a 45 day period. Gastric emptying, perceived gastric fullness, and weight were all measured.  

In the 10-day group, those given the supplement lost slightly more weight than those given the placebo; but in the 45-day group, those given the supplement lost an average of 11.2 pounds compared to less than a pound for those given the placebo.

The researchers then monitored body weight in 22 patients who continued active treatment for 12 months, and reported it "resulted in no further weight loss, nor weight regain in the group as a whole."

So is Zantrex-3 worth a try? The researchers certainly concluded that the supplement they tested was deserving of further, more rigorous study, though no additional trials have been organized.

Given what appeared to be the promising results of the Danish trial, we would like to see further trials of Zantrex-3.