It is the most popular drug in the world. Coffee, tea, chocolate, guarana, soft drinks and some medicines all contain caffeine. Some medicines contain caffeine to give you a "boost" while suffering the cold or flu symptoms. It makes you feel better.
Caffeine can affect most of the body - it stimulates the brain and increases alertness; it causes insomnia, headache, nervousness and dizziness; it releases adrenaline, the stress hormone; it increases heart rate and blood pressure; it increases the rate of breathing; it is a laxative and a fairly strong diuretic; it increases blood sugar levels.
It can work within 15 minutes of taking it and the effects can last for more than six hours.
Caffeine slows the absorption of minerals from food and flushes out the B vitamins.
An 8 oz cup of instant coffee has about 100 mg of caffeine, a cappuccino has something like 50 mg and a decaf has only about 5 mg.
Moderation is the key, a 100 mg caffeine intake a day should present no problems, but high amounts of 900 mg a day and more will cause addiction.
Caffeine can be addictive if taken in large amounts. Then more is needed for the same effect, and if you stop suddenly, there are withdrawal symptoms to contend with.
Withdrawal symptoms include headache, depression, irritability, tiredness, nausea and vomiting. Gradual reduction is the safest way to stop.
Students who take caffeine to keep awake while studying are fooling themselves. It actually makes the memory worse, not better.