Aconine is an alkaloid originally isolated from Aconitum species and active metabolite of aconitine. It inhibits osteoclast differentiation of RANKL-stimulated RAW 264.7 cells and bone resorption in a pit formation assay in a concentration-dependent manner. Aconine also inhibits RANKL-induced activation of NF-κB and NFATc1 in RAW 264.7 cells. In vivo, aconine is toxic to mice when administered intravenously at a dose of 120 mg/kg. It induces flaccid paralysis and toxicity in rats with toxic dose (TD50) and LD50 values of 1.5 and 1.7 μmol per animal, respectively.