EditorialMost people think of melatonin as a natural nod-off aid, kind of like chamomile tea in pill form. Even the name of the popular dietary supplement sounds sleepy — that long “o” sound almost makes you yawn mid-word. But melatonin is also a hormone that our brains naturally produce, and hormones, even in minuscule amounts, can have potent effects throughout the body. (Dadu Shin/The New York Times)