The nopal (or prickly pear) are members of the Opuntia genus of cactus, which are common throughout Mexico and the southwestern United States. The plants have flat, edible pads, or nopales, (which are actually modified branches) with numerous small nodules, or glochids, from which protrude a number of sharp, thorny spines. The plant's flowers, which are usually yellow but may range from orange to purple, form at the edges of the pads, developing into pear-shaped edible fruits, known as tuna.
Nopal pads contain compounds known as flavone glycosides, which may have health promoting properties. Nopal is also rich in dietary fiber and vitamin C.
Nopal is consumed in large quantities as a food with no adverse side effects. Studies demonstrating a blood sugar-lowering effect have used 500 gram doses.