CHICAGO, Apr 4: A study in rats and monkeys suggests an experimental Merck & Co sleep drug may help induce sleep without causing the memory loss and attention problems sometimes seen in the commonly used drugs Ambien and Lunesta, company researchers said yesterday. Experiments in animals suggest Merck’s sleep drug Suvorexant, now before the U.S. Food and Drug Administration, may avoid these side effects, the company said. (agencies)