OBJECTIVE: To evaluate the scientific evidence on guggul for hyperlipidemia including expert opinion, folkloric precedent, history, pharmacology, kinetics/dynamics, interactions, adverse effects, toxicology, and dosing. METHODS: Electronic searches were conducted in nine databases, 20 additional journals (not indexed in common databases), and bibliographies from 50 selected secondary references. No restrictions were placed on language or quality of publications. All literature collected pertained to efficacy in humans, dosing, precautions, adverse effects, use in pregnancy/lactation, interactions, alteration of laboratory assays, and mechanism of action. Standardized inclusion/exclusion criteria were utilized for selection. RESULTS: Before 2003, most scientific evidence suggested that guggulipid elicits significant reductions in serum total cholesterol, low-density lipoprotein (LDL), and triglycerides, as well as elevations in high-density lipoprotein (HDL) [Kotiyal JP, Bisht DB, Singh DS. Double blind cross-over trial of gum guggulu (Commiphora mukul) Fraction A in hypercholesterolemia. J Res Indian Med Yoga Hom 1979;14(2):11-6; Kotiyal JP, Singh DS, Bisht DB. Gum guggulu (Commiphora mukul) fraction 'A' in obesity-a double-blind clinical trial. J Res Ayur Siddha 1985;6(1, 3, 4):20-35; Gaur SP, Garg RK, Kar AM, et al. Gugulipid, a new hypolipidaemic agent, in patients of acute ischaemic stroke: effect on clinical outcome, platelet function and serum lipids. Asia Pacif J Pharm 1997;12:65-9; Urizar NL, Liverman AB, Dodds DT, et al. A natural product that lowers cholesterol as an antagonist ligand for the FXR. Science 3 May 2002 [Science Express Reports]; Nityanand S, Srivastava JS, Asthana OP. Clinical trials with gugulipid. A new hypolipidaemic agent. J Assoc Physicians India 1989;37(5):323-8; Kuppurajan K, Rajagopalan SS, Rao TK, et al. Effect of guggulu (Commiphora mukul-Engl.) on serum lipids in obese, hypercholesterolemic and hyperlipemic cases. J Assoc Physicians India 1978;26(5):367-73; Gopal K, Saran RK, Nityanand S, et al. Clinical trial of ethyl acetate extract of gum gugulu (gugulipid) in primary hyperlipidemia. J Assoc Physicians India 1986;34(4):249-51; Agarwal RC, Singh SP, Saran RK, et al. Clinical trial of gugulipid-a new hypolipidemic agent of plant origin in primary hyperlipidemia. Indian J Med Res 1986;84:626-34; Verma SK, Bordia A. Effect of Commiphora mukul (gum guggulu) in patients of hyperlipidemia with special reference to HDL-cholesterol. Indian J Med Res 1988;87:356-60; Singh RB, Niaz MA, Ghosh S. Hypolipidemic and antioxidant effects of Commiphora mukul as an adjunct to dietary therapy in patients with hypercholesterolemia. Cardiovasc Drugs Ther 1994;8(4):659-64; Ghorai M, Mandal SC, Pal M, et al. A comparative study on hypocholesterolaemic effect of allicin, whole germinated seeds of bengal gram and guggulipid of gum gugglu. Phytother Res 2000;14(3):200-02]. However, most published studies were small and methodologically flawed. In August 2003, a well-designed trial reported small significant increases in serum LDL levels associated with the use of guggul compared to placebo [Szapary PO, Wolfe ML, Bloedon LT, et al. Guggulipid for the treatment of hypercholesterolemia: a randomized controlled trial. JAMA 2003;290(6):765-72]. No significant changes in total cholesterol, high-density lipoprotein (HDL), or triglycerides were measured. These results are consistent with two prior published case reports [Das Gupta R. Gugulipid: pro-lipaemic effect. J Assoc Physicians India 1990;38(12):346]. CONCLUSION: The effects of guggulipid in patients with high cholesterol are not clear, with some studies finding cholesterol-lowering effects, and other research suggesting no benefits. At this time, there is not enough scientific evidence to support the use of guggul for any medical condition. Guggul may cause stomach discomfort or allergic rash as well as other serious side effects and interactions. It should be avoided in pregnant or breast-feeding women and in children. Safety of use beyond 4 months has not been well studied.