The sudden death of a healthy high school senior has focused attention on unregulated caffeine powder. The U.S. Food and Drug Administration is warning consumers to avoid the substance, as it collects more information. A recent autopsy found that 18-year-old Logan Stiner had a lethal amount of caffeine in his system when he died May 27 at his home in LaGrange, Ohio, southwest of Cleveland. A coroner said the prom king and wrestler had as much as 23 times the amount of caffeine in his system found in a typical coffee or soda drinker. Health officials worry about the powder's potential popularity among exercise enthusiasts and young people seeking an energy boost. It's sold as a dietary supplement, not subject to the same federal regulations as certain caffeinated foods.