Source: Science Magazine
In an article introduced as "Health Food Supplement Lives Up to Hype, Extract from India's guggul tree lowers cholesterol, published in the May 2nd issue of "Science" magazine, the authors show that guggul resin extracts lower LDL levels in humans. The sterol guggulsterone specifically appears to be the active agent, as an antagonist of the farnesoid X receptor (FXR), which is activated by bile acids.
The authors suggest that inhibition of receptor activation accounts for the hypolipidemic effect.