Some powerful and complex painkilling drugs have just been discovered—in a place where you would least expect to find them. Endorphins and their component enkephalins are manufactured in the brain, and perform the same painkilling function as analgesics like morphine. NOVA explores some physiological mysteries, such as why acupuncture works, and how placebos can relieve symptoms, and shows how endorphins could revolutionize the treatment of pain, depression, and even schizophrenia.