Ephedra-free weight loss dietary supplements containing bitter orange (Citrus aurantium), a botanical source of the adrenergic amines synephrine and octopamine, have quickly emerged on consumer markets to replace banned ephedra products. These supplements may have some of the health risks associated with ephedra, but studies in humans are lacking. Our aim was to characterize the pharmacokinetics and cardiovascular effects of C. aurantium dietary supplements.

Ten healthy adult nonsmokers participated in a randomized, double-blind, placebo-controlled, three-arm crossover study. Single doses of C. aurantium (Advantra Z) containing 46.9 mg synephrine, Xenadrine EFX, a multi-component formulation containing 5.5 mg synephrine, and placebo were administered with a one-week washout.

Compared with placebo, Xenadrine EFX but not Advantra Z increased systolic and diastolic blood pressure with peak changes from baseline at 2 hours of 9.6 ± 6.2 mm Hg systolic (P = 0.047), and 9.1 ± 7.8 mm Hg diastolic (P = 0.002). Heart rate was increased from baseline at 6 hours compared with placebo (16.7 beats per minute with Xenadrine EFX, P = 0.011; 11.4 beats per minute with Advantra Z, P = 0.031). Dose-adjusted synephrine pharmacokinetics were similar between treatments with t_max = 90 min, t_1/2 = 3.0 hours, V/F = 16347 L, and CL/F = 88.9 L/min for Xenadrine EFX.

Ephedra-free weight loss supplements have significant cardiovascular stimulant actions, similar to ephedra. These effects are not likely caused by C. aurantium alone, because an eightfold higher dose of synephrine (Advantra Z) had no effect on blood pressure, but may be attributable to caffeine and other stimulants in the multi-component formulation