What happen when caffeine enters the body??
Caffeine is well absorbed from by the stomach and intestine, and peak caffeine in blood occur about 45 - 60 minutes after ingestion. Once the caffeine is in the blood stream, caffeine causes stimulant effects to the brain. There are some other physiologic effects will occur, like high blood pressure, pulse rate, and stomach acid production increased, fat stores broke down, and fatty acids are released into the blood stream. These effects can last from a few hours to twelve hours.
Caffeine in Sports 
Caffeine does not appear to benefit short term or high intensity exercise, caffeine can only enhance performance in endurance sports. Caffeine has many benefits for different types of athletes. There are many athletes believe caffeine can enhance both physical and mental performance because it decrease fatigue in athletes. Caffeine has been proven to stimulate the central nervous system. Caffeine stimulates the central nervous system at high levels (medulla and cortex), and also has the ability to reach the spinal cord in larger ingestion. The effect of caffeine in the cortex is a clearer thought process and this can gives people a greater ability of concentration for 1-3 hours.
Caffeine and Health 
In making a decision whether or not to use caffeine, it is important to consider the side effects on health. These can be divided into short term and long term. The short term affects of caffeine are better than the long term effects. Because caffeine increases the production of stomach acid, it will worsen ulcer symptoms or cause heartburn, poor sleep, and anxiety. Regular evening use of caffeine will stop the body of proper sleep, resulting in lack of energy and fatigue
Caffeine Withdrawal
Abortion of taking caffeine in a regular user may lead to caffeine withdrawal symptoms. The most common symptoms are headache and fatigue. The headache may begin as soon as 18 hours following the last ingestion of caffeine and will worsen with exercise.
Side effects of taking caffeine
The benefits of using caffeine are different for each individual. It is because of differences in metabolism, diet, how often you use caffeine are some of the factors that to determine how an individual will react to it. Some athletes may actually experience decrease in performance due to the side effects of caffeine. Also caffeine does not appear to alter water balance or body temperature during exercise. Dehydration is a potential concern because caffeine is a diuretic effect. Caffeine increases the blood flow in the kidneys and at the same time stop the reabsorption of sodium and water. Also caffeine will weaken the detrusor muscles in the bladder, which provokes the need to urinate. This might decrease the performance to an athlete. Some athletes may experience abdominal cramp and diarrhea due to the large intestine contractions caused by caffeine. The combination of dehydration and cramping can have negative effects on performance. Apart from this, caffeine causes lots of other side effects like sleep deprivation, nausea, cramping, anxiety, fatigue, headaches, and gastrointestinal instability, so caffeine has more side effects which can affect performance.
Drug testing
The International Olympic Committee currently lists caffeine as a restricted drug. When the urinary levels above 1000mg of caffeine (about 8 cups of coffee) would be required to exceed the current IOC, this are viewed an attempt at doping by the athlete.
Conclusion
I have mentioned both beneficial and side effects of regular use of caffeine, I am not suggesting that athletes use caffeine or not. All I want to tell people is do consider carefully before usage of caffeine, it might make you train or compete harder, but it can also make you suffer from the side effects or banded from any ofcompetition.
