Looking for an energy pick-me-up? Avoid pure caffeine powder supplements sold online, warns the U.S. Food and Drug Administration (FDA), which recently linked the substance to the demise of at least two young men this year, the Wall Street Journal reports.

Powdered caffeine is often marketed as an athletic performance enhancer or a weight-loss aid and is most commonly used by teenagers and young adults. The dietary supplement can be bought online for at little as $10 for 8 ounces. (One teaspoon of the pharmaceutical-grade drug is equivalent to 25 cups of coffee.)

Federal health officials warn that just small amounts of powdered caffeine can lead to a rapid heartbeat, seizures, coma and death, even among the healthiest people who take it.

In May, Logan Stiner, an 18-year-old high school student from Ohio died after taking some caffeine powder his parents later found in his bag. James Wade Sweatt, a 24-year-old from Georgia, who started taking the powder to try to avoid the sugars found in energy drinks, died in June after falling into a caffeine-induced coma.

As a response to the tragedies, health advocates at the Center for Science in the Public Interest petitioned the FDA earlier this month to ban retail sales of pure caffeine as a dietary supplement. Federal health authorities said they are now considering regulatory action to address these concerns.

Energy drinks can also lead to major health risks in kids. Click here for more information.