Here's what Derek Cornelius says about guggul (keep in mind that he's the president of Syntrax - so there's bound to be a bias to this info....but whatever...)
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Guggul is a tree which exudes a resinous sap out of incisions that are made in its bark. This resin has been used for centuries as part of India's traditional medicine called Ayurveda. In our modern world of advanced chemistry, this resinous sap is processed and purified, and then standardized for a given amount of its active constituents-Z and E Guggulsterones. These two compounds are plant sterols with a high degree of human bioactivity and have been shown in studies to affect many biological processes including thyroid metabolism, cholesterol management, and dermal (skin) function. In each of these areas, Guggulsterones were shown in studies to be highly effective modulators with near drug-like potency.
When the thyroid gland is stimulated, it produces more thyroid hormones such as thyroxin. These thyroid hormones have a profound effect on the rate of metabolism including a direct catabolic effect on adipose tissue. Practically, this means that Guggulsterones will stimulate your thyroid to produce more thyroid hormones which in turn will raise your metabolic rate and burn more fat! Guggulsterones by themselves have been shown to work very well for fat loss but I have found a combination that is nothing short of amazing-Guggulsterones and an ECA stack.
The dosage one should take is 30-60mg three times per day with meals.
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Again, keep in mind that Cornelius is really pushing Adipo here - but I have heard a lot of people claim to have great success stacking Guggulbolic w/ Adipokinetix......but who knows...
Some products I know of that contain guggul:
of course there's Guggulbolic - by Syntrax
Thyrostack - by MuscleLinc
Thyroburn - by Sportpharma
Thermogenic Thyrolean - by Prolab
There are lots of others - just ask around - not sure which is best or most effective, etc......