Whether you consume it via food or medications, caffeine is a central nervous system stimulant that can cause both positive and negative effects in your body. Caffeine is a natural substance: more than 60 plants contain the compound, but it also can be synthetically manufactured to add to foods and drinks, according to the United States Food and Drug Administration. Because caffeine stimulates your central nervous system, it can have both positive and negative effects on your body, depending upon your unique sensitivity to caffeine-containing products.
Chemical Effects
As a central nervous system stimulant, caffeine effects your brain, spine and nerves. Caffeine works by blocking the actions of two chemicals that set off a chain reaction in the body. Caffeine first blocks phosphodiesterase, which typically is responsible for breaking down a chemical known as cyclic adenosine monophosphate. When caffeine keeps these chemicals from breaking down, the body is prompted to release chemicals known as norepinephrine and epinephrine, which trigger the "fight or flight" chemical reaction in the body.
Initial Reactions
Epinephrine and norepinephrine trigger a number of physical reactions in the body. The first is to raise your heart rate. You may notice your heart beating slightly faster when you consume caffeine. The faster heartbeat sends more oxygen-filled blood to your tissues and brain. This can make you feel more awake, temporarily boosting your concentration and alertness. However, the sped-up reactions in your body can also cause you to feel excitable, anxious and nervous due to your heightened heart rate. You will notice these effects most within one hour, and caffeine takes about four to six hours to fully leave your system, according to the FDA.
Adverse Reactions
While caffeine temporarily halts the breakdown of certain chemicals in your body, when caffeine leaves your body you may feel the effects are more pronounced. For example, caffeine can increase the amount of acid released in your stomach, which may cause upset stomach or heartburn. Caffeine also is a natural diuretic, which means you may notice you are urinating more and may feel thirstier than usual. As the caffeine starts to leave your body, you may start to feel even more fatigued than you did before you consumed any caffeine.
Sensitivity
While most people can consume a moderate amount of caffeine, which is between 200 and 300mg per day or the equivalent of two to four cups of coffee, without too many adverse side effects, some people are more sensitive to caffeine's effects than others. Caffeine can cause unpleasant physical symptoms such as inability to sleep or muscle tremors. If you find you are more sensitive to the effects of coffee, soda, chocolate or caffeine-containing medications, you may wish to avoid or reduce your caffeine intake.
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