This is the alkaloid of tea and coffee, and is mostly used as the citrated caffeine.
It has no action on the skin or mucous membranes, but is readily absorbed from the latter.
It stimulates and strengthens the heart, raises the blood pressure, stimulates the brain, and increases the activity of the kidneys. Poisonous doses cause great cerebral and nervous excitation, rapid heart, and respiratory failure.
It is excreted in the urine.