Caffeine--induced psychiatric disorders

Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a psychoactive stimulant drug and a mild diuretic (1). In humans, caffeine is a central nervous system (CNS) stimulant (2), having the effect of temporarily warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks, enjoy great popularity. Caffeine is the world's most widely consumed psychoactive substance, estimated at 120,000 tonnes per annum (3), but unlike many other psychoactive substances, it is legal and unregulated in nearly all jurisdictions. The half-life of caffeine--the time required for the body to eliminate one-half of the total amount of caffeine--varies widely among individuals according to such factors as age, liver function, pregnancy, some concurrent medications, and the level of enzymes in the liver needed for caffeine metabolism. In healthy adults, caffeine's half-life is approximately 3-4 hours. The average daily consumption of caffeine among Americans is 219 mg. (4) Adults receive nearly three quarters of their daily caffeine from coffee. Children receive one half of their caffeine from soft drinks. Energy drinks represent a fast-growing beverage market. A combination of caffeine and herbal ingredients are touted as providing an energy boost. Energy drinks vary in the amount of caffeine included in their formulations and can range from around 50-300 mg. Consumers seeking the activating qualities of caffeine in pill form can find many preparations, the more well known having 200 mg. Individuals worldwide consume about 76 mg of caffeine per day. Most people experience no behavioral effects with less than 300 mg caffeine. Sleep is more sensitive and can be disrupted by 200 mg caffeine. At doses exceeding 1 g per day, susceptible individuals experience toxic effects. The caffeine content in some common sources of caffeine is listed below (Table1).

Caffeine Addiction

Although caffeine does not produce with life-threatening health risks commonly associated with the use of classic drugs of addiction such as cocaine, heroin and nicotine, some caffeine users report becoming "addicted" to caffeine in the sense that they report an inability to quit or to cut down their caffeine use. The mood altering effects of caffeine depend on the amount of caffeine consumed and whether the individual is physically dependent on or tolerant to caffeine.

In caffeine non-users or intermittent users, low dietary doses of caffeine (20-200 mg) generally produce positive mood effects such as increased well-being, happiness, energetic arousal, alertness, and sociability. Among daily caffeine consumers, much of the positive mood effect experienced with consumption of caffeine in the morning after overnight abstinence is due to suppression of low grade withdrawal symptoms such as sleepiness and lethargy. Large caffeine doses (200 mg or greater) may produce negative mood effects. Although...