kwanny, i was actually wondering about this too because i still have a bottle left over from last year. i dont want to waste it.
i found this from christian finn
Caffeine can raise your metabolic rate, boost muscle strength, improve performance during short-term, high-intensity exercise and increase the number of fat calories you burn both during and after exercise.
By itself, caffeine has a minor role in fat loss. When used in conjunction with other fat loss methods (such as exercise), it does make fat loss faster and easier.
Although caffeine does reduce insulin sensitivity, this is more of a concern for people combining the habitual consumption of caffeine (in the form of coffee, for example) with a high-carbohydrate diet, rather than those using caffeine before exercise as a way to increase fat oxidation and give themselves a physical and mental "kick".
The majority of evidence supports the use of approximately 5 milligrams of caffeine per kilogram (2.3 milligrams per pound) of bodyweight. Although higher doses (up to 10 milligrams per kilogram of bodyweight) have been studied, they provide little in the way of additional benefit. In fact, lower doses (200-300 milligrams) may be just as effective [40].
If you've never used caffeine before exercise, begin with a low dose (50-100 milligrams) to assess your tolerance. Then, increase the dose gradually. When you consume caffeine on a daily basis, its beneficial effects on exercise performance are slightly reduced but not eliminated completely [34]. Fat metabolism is also increased to a similar extent in both users and non-users of caffeine [47].
A recent safety review shows that up to 6 milligrams of caffeine per kilogram of bodyweight daily has no adverse effect on health. However, reproductive-aged women and children may need to moderate their caffeine intake. Based on the available evidence, reproductive-aged women should consume a maximum of 4.6 milligrams of caffeine per kilogram of bodyweight, while children should consume a maximum of 2.5 milligrams per kilogram of bodyweight [37].
Caffeine does raise blood pressure and cortisol levels, a response which is exaggerated by the stressful events of normal daily life [55, 56]. If you have high blood pressure, a lot of caffeine isn't a good idea, particularly if you're under a lot of stress. Women using oral contraceptives will need to be even more careful, as it takes their body a lot longer to metabolize the caffeine.
Caffeine is also thought to lower testosterone levels, though the evidence is scant. One trial, published in the American Journal of Epidemiology, shows that as caffeine intake rises, bioavailable testosterone levels drop [52]. However, the study only looked at white postmenopausal women aged 42-90 years. Whether the same link holds true for all men and women of all ages is open to debate.
Although caffeine does stimulate a mild loss of water, there is no evidence to show that this causes any kind of fluid-electrolyte imbalance that is detrimental to exercise performance or your health, as long as you drink enough water [33].
While coffee does contain high levels of caffeine, it also contains a number of other compounds that may interfere with the effects of caffeine. Most of the studies cited in this article used caffeine capsules, rather than coffee, tea or caffeinated drinks.
