Regular, heavy caffeine use can lead to tolerance and dependence.
Tolerance - this means that a person needs more of the drug to achieve the same effects they did previously with smaller amounts.
Dependence - this occurs when someone finds it very difficult to stop or reduce their caffeine consumption.
Withdrawal - occurs when someone who is dependent on caffeine decides to cut down or stop using it. Symptoms include severe headaches, poor concentration, flu-like symptoms, irritability, and tiredness/fatigue. These symptoms usually begin 12 to 24 hours after the last dose of caffeine and may last for up to one week.