Caffeine is a bitter substance that occurs naturally in coffee, tea and cocoa plants and adds a "kick" to sodas, energy drinks and supplements. An estimated 80 to 90 percent of Americans consume caffeine habitually, according to the Johns Hopkins Bayview Medical Center, making it the most commonly used mood-altering drug. And about 15 percent of consumers stop caffeine use because of unpleasant side effects. Shakiness affects some, but not all, caffeine users.
Function
Caffeine stays in your body hours after consumption, according to the University of Washington. After reaching your digestive system, it enters your bloodstream where it is transported throughout your body. Caffeine interferes with a chemical in the brain called adenosine, which helps the body relax. In other words, caffeine can block your ability to experience calm or sleepiness. Because of its stimulant properties, caffeine also increases your heart rate. Both of these properties can contribute to shakiness and related symptoms, such as nervousness, restlessness, irritability and difficulty sleeping.
Typical Effects
If you are a healthy adult, chances are that moderate caffeine intake, or 200 to 300 mg of coffee per day, will not cause harmful effects, according to MayoClinic.com. You may feel more alert, happier or more sociable and find it easier to concentrate or perform work, schoolwork or fitness-oriented tasks well. Consuming excessive amounts, or 500 mg or more per day, however, increases your risk for side effects.
Considerations
If you are particularly sensitive to caffeine shakiness, then agitation and other complications can stem from small amounts, such as one cup of tea or coffee. Not drinking caffeine routinely, having an anxiety disorder, being male or using certain medications can make you more susceptible to caffeine's adverse effects, according to MayoClinic.com. And various caffeinated products, such as energy drinks and dietary supplements, contain additional stimulants, such as ginseng, green tea extract or guarana, that can worsen or cause additional side effects.
Suggestions
If you have a normal response to caffeine, meaning a small amount does not trigger side effects, stick to 300 mg -- the amount in two to three cups of coffee -- per day. An average cup of tea contains 50 mg caffeine. Energy drinks can contain up to 300 mg per 8.4-oz. can. If you wish to reduce your caffeine intake, do so gradually to avoid headaches, irritability and other withdrawal symptoms. If your symptoms after consuming or stopping caffeine use are severe, seek medical guidance.
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