The FDA is cracking down on distributors of pure powdered caffeine. On Tuesday, the agency released a statement announcing that it fully intends to “aggressively monitor the marketplace for pure powdered caffeine products and take action as appropriate.” This is no empty threat. Warning letters were issued to five distributors of the product on August 27th. The FDA found the products to be adulterated within the meaning of the Food, Drug, and Cosmetic Act because they contain amounts of caffeine that could be lethal to consumers, and require the use of a precise scale to distinguish a “safe serving from a potentially lethal amount.” As a result, the agency concluded that the products present “a significant or unreasonable risk of illness or injury under the conditions of use recommended or suggested in the labeling.”

Pure powdered caffeine products are 100% caffeine and a single teaspoon is the equivalent to approximately 25 cups of coffee. According to the FDA, there is a small difference between a safe amount and a toxic dose of pure powdered caffeine. Moreover, household measuring tools, such as teaspoons, lack the requisite precision to accurately measure the products. The products referenced in the warning letters contain hundreds or thousands of servings of the stimulant.

Two young men died in 2014 after using these products. After these deaths, the FDA issued a statement warning consumers of the products’ potentially harmful effects. However, the agency has experienced pressure to do more. Just last month, U.S. Senator Sherrod Brown (D-OH) and five other senators wrote a letter urging the FDA to ban the sale and marketing of powdered caffeine for retail use. Ohio has already enacted legislation to ban the sale of powdered caffeine in the state, where pure caffeine overdoses have been responsible for more than 200 hospital admissions, including five life-threatening cases in 2014.

The companies have 15 business days to respond to the warning letters. Retailers should think twice about selling these products.