AP Photo

When Matthew Penbross woke on a morning in August 2007—a day in which he’d be competing in motocross races near Port Macquarie, Australia—he wanted to be prepared. To improve his reaction speed on the start line, the 28-year-old began drinking Red Bull Energy Drinks soon after he rolled out of bed. All told, he would drink seven or eight of the caffeinated beverages within a seven-hour period.