Caffeine in the form of coffee/tea is consumed regularly by over 80 percent of adults. Caffeine is also present in tea, cola drinks, cocoa, chocolate, and many over the counter cold preparations.

A rough guide to calculating caffeine intake is as follows:

100 to 150 mg of caffeine in a cup of coffee. Tea is about half as strong. A glass of cola is about one third as strong. Most prescription drugs and OTC medications containing caffeine are one third to one half the strength of a cup of coffee. Two exceptions to this are migraine medications and OTC stimulants that contain 100 mg in a tablet.

The clinical effects of an acute dose of caffeine (50 to100 mg) include increased alertness, a sense of well-being, and improved verbal and motor performance. It is because of these effects that persons become psychologically dependent on caffeine. In addition, caffeine increases frequency of urination, heart rate, intestinal motility, acid secretion in stomach, and blood pressure.

Tolerance: Chronic users develop tolerance to the effects of caffeine. The average adult consumes more that 500 mg of caffeine a day but usually in the markedly diluted form of brewed coffee. Caffeine intake over 500 mg increases the risk of developing intoxication, however, some persons can consume to 3 g a day without complaints.

Signs of caffeine intoxication include anxiety, psychomotor agitation, restlessness, irritability, and psychophysiological complaints, such as muscle twitching, flushed face, nausea, increased frequency of urination, gastrointestinal complaints, and disturbed sleep. Intoxication can occur with daily doses of as little as 250 mg of caffeine, but most people require much larger doses. At levels of more than 1 g per day, there may be disturbed flow of thought and speech, disturbed heart rate, inexhuastibility and agitation. Tinnitus and flashes of light have been reported. With doses of 10 g or higher, grand mal seizures and respiratory failure can lead to death.

Various studies have reported that from 25 to 100 percent of caffeine users experience symptoms of withdrawal on discontinuation of intake. Withdrawal symptoms usually have their onset in 12 to 24 hours, peak in 20 to 48 hours, and last approximately one week. The major symptoms of caffeine withdrawal are headache and fatigue. Other symptoms include anxiety, impaired psychomotor performance, and nausea, vomiting, and craving for caffeine. Anhedonia, irritability, and depression can occur in some persons, especially those with a long history of relatively high caffeine intake.

Chronic caffeine use stimulates gastric hyperacidity, which can aggravate ulcer disease and can lead to the development of disturbed heart rate, especially in persons with preexisting heart disease. Some studies have demonstrated that the elimination of caffeine produces clinical improvement in women with fibrocystic disease. Users of excessive amounts of caffeine have been misdiagnosed as suffering from generalized anxiety disorder and have been treated unnecessarily with antianxiety agents.

Caffeine intoxication or withdrawal is diagnosed on the basis of a detailed history to confirm significant caffeine sources other than coffee in addition to signs and symptoms of anxiety in the case of intoxication and headache or lethargy in the case of withdrawal. The clinician needs to rule out general anxiety disorder, mood disorder, sleep disorder, and thyroid disease, all of which may coexist.

Treatment consists of abstinence, which can be accomplished if the person in highly motivated. Antianxiety agents are not needed except in rare cases, and simple pain killer, such as aspirin, may be used to treat headache. Water and decaffeinated coffee and soft drinks can be substituted for caffeinated beverages. Withdrawal usually takes four to five days.