The Food and Drug Administration has issued warning letters to five distributors of pure powdered caffeine, saying the products put consumers at risk of illness or injury.
The letters are dated Aug. 27. They follow the overdose deaths last year of two young men from Ohio and Georgia.
The FDA says a teaspoon of powdered caffeine is roughly equivalent to 28 cups of coffee, and the difference between a safe and toxic amount is very small.
The packages of pure caffeine referenced in the letters contain hundreds or thousands of servings. The agency says such packaged quantities are potentially lethal to many consumers.
The FDA had warned consumers last summer to avoid pure powdered caffeine. Officials say a safe amount can be nearly impossible to measure with common kitchen tools.