WASHINGTON (Reuters) - A new pill that aims to keep alcoholics from drinking again after they have quit could hit the shelves by the end of this year after U.S. health officials approved the drug on Thursday. The drug, called Campral, may not work for people who are actively drinking when they start taking the pill or who are abusing other substances, the U.S. Food and Drug Administration said in a statement. It was not clear how the pill worked, health officials said, but studies showed more patients who took the drug stayed away from drinking compared to those who...