Researchers at the Yale School of Medicine have called it "the magic drug," able to halt severe depression and suicidal thoughts in patients within a matter of hours. Ketamine, used as an anesthetic in human and veterinary medicine, has emerged in the past few years as a promising, rapid-acting antidepressant. When administered intravenously at low doses, it can lift symptoms of deep depression within hours, for seven to 10 days. Typical antidepressants, which act on the neurotransmitter serotonin, take a month or more for full effect.