Caffeine is a CNS stimulant. Many adverse reactions to caffeine are an extension of caffeine's pharmacologic actions. At therapeutic or nontoxic doses, caffeine can cause tremor, sinus tachycardia, and heightened attentiveness. Other adverse reactions include diarrhea, excitement, palpitations, insomnia, headache, and muscle twitches. Cardiac arrhythmias, seizures, and delirium are possible after deliberate overdoses.
Caffeine is a mild diuretic.
Polyuria can occur. In 1992, a distinct caffeine withdrawal syndrome was described. Patients who consume or receive caffeine daily for several weeks experience notable physical and psychiatric responses including lethargy, anxiety, dizziness, or headache. Caffeine occurs naturally in tea, coffee, cocoa, and chocolate, and is added to many soft drinks. Generic forms of caffeine are available, and can be obtained without a prescription.