The FDA says that 400 mg of caffeine each day is the limit for healthy people over 17 years old, and this equals about four (8 fl. oz.) cups of coffee, 10 (8 fl. oz.) cans of cola, or simply about a couple of Monster Energy drinks! It's important not to exceed this amount because consuming more than 400mg can lead to unpleasant side effects such as jitteriness, insomnia, and heart palpitations, among others.