Although most people can drink two

Although most people can drink two to four cups of coffee a day without experiencing harmful effects, consuming excess caffeine can cause several problems. According to MedlinePlus, drinking too much coffee can cause dehydration, headaches and dizziness and can make you jittery and shaky. In addition, excess coffee consumption can make your heart beat faster or result in abnormal heart rhythms. It may also affect your ability to fall asleep and stay asleep.