Coffee and tea are very popular beverage choices. However, they contain caffeine – a substance that can boost metabolism, mood, and mental and physical performance. Many people drink caffeine for mental alertness, migraine, memory, and athletic performance. In most cases, drinking these beverages in low to moderate quantities is considered safe, but high doses of caffeine may have unpleasant and sometimes even dangerous side effects. So it’s advised to limit caffeine intake as much as possible. Side effects of caffeine Experts believe healthy adults can drink up to 400 milligrams of caffeine daily. It means nearly 4 cups of brewed coffee a day is safe. However, one must know the possible side effects of caffeine, some of which are listed below. Insomnia One of the most prized qualities of caffeine is its ability to help people stay awake. But excessive amounts of caffeine can make it challenging to get restorative sleep. Furthermore, studies have found that high doses of caffeine decrease total sleeping time, especially in older adults. In addition, caffeine taken later in the day may interfere with sleep as its effects take several hours to wear off completely. Rapid heart rate High amounts of caffeine also possess stimulatory effects that can increase heart rate.