 Many of these caffeinated drinks can you have before it's dangerous. According to recommendations from the FDA, you're going to want to stick to five or less eight ounce cans of Red Bull a day, while 15 in a short period of time can be toxic. While you can have two cans of Celsius in a day and still be safe, while six can be toxic, you can only have two of these tiny bottles to stay in the safe range, and you for sure don't want to get up to six. A medium cup of Dunkin' Coffee packs more of a punch than you think. You shouldn't have more than 1.9 cups in a day to be safe, with 5.7 in a short period of time potentially causing toxicity. But you should be most careful with Starbucks's Nitro Cold Brew. You can't even have one and a half grande cups of it and stay in the safe range, and just over four cups could lead to toxic side effects like seizures.