Ergotamine is an ergot alkaloid occurring naturally in the plant Claviceps purpurea. It has vasoconstrictive action and is used therapeutically in the treatment of vascular headaches, such as migraine. Ergotamine is distinguished from the other three main classes of ergot alkaloids, all of which also have strong oxytocic activity, and some which also have therapeutic value. Ergotamine given orally to laboratory animals has not shown teratogenic potential. Doses of up to 300 mg/kg/day given to mice during organogenesis caused a reduction in fetal weight and retarded ossification. In the human, a variety of cases recording developmental toxicity apparently resultant from treatment with ergotamine were published. Of the 28 cases described in the literature, at least 22 depicted a diversity of congenital defects, consistent with a disruptive vascular mechanism, due presumably to the known vasospasmic action of the drug. Ergotamine is one of the largest human developmental toxicants. This polar compound is slightly hydrophobic.