Caffeine is one of the most common and effective natural stimulants; it can be found in tea, coffee, chocolate and energy drinks. Caffeine enters bloodstream within 15 minutes and induce its stimulant effects within 1 hour for 5 – 10 hours. So, caffeine is mainly used to promote brain functions and to improve memory and concentration.
On the same context, caffeine has the following health benefits:
    It can be used to relieve headache.
    It has anti-inflammatory effects, so it's believed that moderate intake of caffeine reduces the risk of type 2 diabetes as well as many cardiovascular diseases.
    It reduces the risk of Alzheimer disease.
On the other side, overconsumption of caffeine may induce many negative health effects, such as; nausea, headache, dehydration, tremors, insomnia, heartburn and diarrhea. Also, it's found that excessive intake of caffeine could be responsible for many serious health conditions, such as:
•    Arrhythmias (tachycardia or bradycardia).
•    Cardiac ischemia.
•    Seizures.
•    Muscle damage.
In conclusion, caffeine can be included in your diet, but it should be consumed in moderation.