Theobromine, also known as xantheose, is the principal alkaloid of the cacao bean. It is in the methylxanthine class of chemical compounds. Methylxanthines naturally occur in many different plant species which includes: caffeine (the primary methlyxanthine in coffee) and theophylline (the primary methylxanthine in tea). Theobromine is the primary methylxanthine found in products of the cocoa tree, theobroma cacao.

Theobromine is mildly diuretic (increases urine production), is a mild stimulant, and relaxes the smooth muscles of the bronchi in the lungs.

Theobromine has been used as a drug for its diuretic effect, particularly in cases where cardiac failure has resulted in an accumulation of body fluid. Because of its believed ability to dilate blood vessels, theobromine also has been used to treat high blood pressure.