Caffeine is a trimethylxanthine in which the three methyl groups are located at positions 1, 3, and 7. A purine alkaloid that occurs naturally in tea and coffee. It has a role as a geroprotector, a mutagen, a central nervous system stimulant, a psychotropic drug, a diuretic, a xenobiotic, an EC 3.1.4.* (phosphoric diester hydrolase) inhibitor, an EC 2.7.11.1 (non-specific serine/threonine protein kinase) inhibitor, an adenosine A2A receptor antagonist, an adjuvant, a food additive, a ryanodine receptor agonist, an adenosine receptor antagonist, a mouse metabolite, a plant metabolite, a fungal metabolite, an environmental contaminant and a human blood serum metabolite. It is a purine alkaloid and a trimethylxanthine.