Excessive caffeine consumption can lead to several potential side effects, including increased heart rate, anxiety, digestive issues, and sleep disturbances. High intake can also cause headaches, jitters, and in extreme cases, even cardiovascular problems. Tolerance can develop over time, causing individuals to consume higher amounts to achieve the same effects. The recommended maximum is about 400 mg per day for most adults, equivalent to around four 8-ounce cups of brewed coffee. Monitoring intake is crucial, as individual sensitivity to caffeine varies significantly.