The stimulatory effects of caffeine may begin as early as 15 minutes after ingesting the drug and last as long as six hours.
In moderate doses, caffeine helps to increase alertness and reduces sleepiness.
However, regular ingestion of excess amounts of caffeine can lead to problems such as poor concentration, nervousness, heartburn, constipation and diarrhea.
Longer-term effects may include sleep deprivation, impaired judgement, emotional fatigue, mood swings, depression and anxiety.