Theobromine-d6 is intended for use as an internal standard for the quantification of theobromine by GC- or LC-MS. Theobromine is a methylxanthine alkaloid and derivative of caffeine that has been found in cocoa beans and has diverse biological activities. It is an adenosine A1 receptor antagonist. Theobromine increases AMPK phosphorylation and inhibits adipocyte differentiation, ERK and JNK phosphorylation, and IL-6 and TNF-α production in 3T3-L1 preadipocytes cultured in differentiation medium. It inhibits decreases in renal cortex SIRT1 activity and increases in NADPH oxidase-dependent reactive oxygen species (ROS) production, as well as reduces kidney hypertrophy and albuminuria in a spontaneously hypertensive rat model of streptozotocin-induced diabetes when administered at a dose of 5 mg/kg per day.3 Theobromine is toxic to dogs with an LD50 value of 250 to 500 mg/kg.