Similar compounds are also found in the Coca plant. Fencamfine is another CNS stimulant with a polycyclic structure similar to cocaine. Caffeine is one of a group of alkaloids called methylxanthines which inhibit the degradation of the second messenger cAMP by the enzyme phosphodiesterase. The cAMP system couples the reception of a neurotransmitter at the far side of synapses to the sequential depolarization pulse down the next nerve. Caffeine also antagonizes presynaptic adenosine receptors, facilitating catecholamine release.
Caffeine occurs naturally in the coffee bean, tea leaves, guarana, and other plants.
It is probably the most-used of all psychoactive drugs. It acts as a vasodilator in the CNS, reducing blood pressure and headache symptoms. It also imparts diuretic and blood-thinning qualities and may reduce formation of kidney stones by increasing urination. It may thus enhance athletic performance. Cafaminol and caffeic acid also occur in the coffee plant.