Pharmacology

The pharmacokinetic profile of caffeine is well known. Taken orally, caffeine is almost completely absorbed by the stomach.^2,3 Since it is lipid soluble, caffeine permeates the blood-brain barrier; it becomes pharmacologically active 6-8 minutes after ingestion and is fully active within 30 minutes.³ Caffeine has a half-life of 3-5 hours,⁴ and it is eliminated via the kidneys. The half-life and clearance time of caffeine are increased in patients with liver disease.⁵

Caffeine exhibits a range of pharmacodynamic effects. For example, by rapidly decreasing gastric pH, caffeine promotes the absorption of analgesic medications.^6-8 Caffeine also constricts intracranial and extracranial cerebral blood vessels, providing a benefit in migraine patients.^9-11 Caffeine consumption has been shown to decrease the duration of theta (slow-wave) activity on electroencephalogram for approximately 5 hours after ingestion.¹² Caffeine intake does not appear to improve memory, but various studies have shown that test responses are faster and more accurate when caffeine is administered.^13-16 Response to caffeine's effects may be modified by the personality type.¹⁷ Smoking decreases the duration of caffeine's physical effects by increasing its rate of clearance.^18,19 Certain drugs delay the elimination of caffeine, including oral contraceptives,²⁰ cimetidine,²¹ disulfiram,²² and alcohol.²³