According to a new study from the University of Adelaide, drinking more than two energy drinks daily can lead to an abnormal heart rhythm, heart palpitations, and a fast heartbeat. Even though healthy adults can have up to 400mg of caffeine per day, it is not advised to have more than 2 Red Bulls a day. Excessive intake, which is more than 5 Red Bulls, can increase your risk of caffeine overdose and have other serious side effects. In people with undiagnosed heart conditions, it could trigger a heart attack. Teens should limit their caffeine intake to less than 100mg daily, which translates to one can of Red Bull.