Caffeine is a mild stimulant present in coffee, tea and cola as well as in tablet form and in special ‘energy’ drinks. Caffeine can even be found in chocolate and some medicines.. It can improve reaction time and feelings of alertness for short periods.
Caffeine acts as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness. Caffeine raises blood pressure so it isn't good if you have high blood pressure or heart disease.
Regular use of caffeine does cause mild physical dependence, if you stop taking caffeine abruptly; you may have symptoms for a day or more, especially if you consume two or more cups of coffee a day. Symptoms of withdrawal from caffeine include:
Ordinary consumption has low health risks, even when carried on for years, there may be a modest protective effect against some diseases, including; Parkinson’s disease, heart disease, and certain types of cancer.
A caffeine overdose can result in a state of central nervous system over-stimulation called caffeine intoxication. This syndrome typically occurs only after ingestion of large amounts of caffeine, well over the amounts found in typical caffeinated beverages and caffeine tablets (e.g., more than 400–500 mg at a time).
The symptoms of caffeine intoxication are comparable to the symptoms of overdoses of other stimulants: they may include restlessness, fidgeting, anxiety, excitement, insomnia, flushing of the face, increased urination, gastrointestinal disturbance, muscle twitching, a rambling flow of thought and speech, irritability, irregular or rapid heart beat In cases of much larger overdoses; mania, depression, lapses in judgment, disorientation, disinhibition, delusions, hallucinations, or psychosis may occur, and rhabdomyolysis (breakdown of skeletal muscle tissue) can be provoked. Extreme overdose can result in death.
Caffeine should only be used occasionally and shouldn’t be relied on it to keep you awake. Persons taking caffeine or other stimulants, should consider what might happen when its effects wear off e.g. when you are operating machinery or driving.