Chocolate Interactions

Caffeine and theobromine from chocolate are competitive antagonists at A1 and A2A adenosine receptors. When intravenous adenosine is used for cardiac stress testing or to terminate supraventricular tachycardia, recent methylxanthine intake can blunt its effects and lead to a falsely negative test or failure to convert the arrhythmia.

The caffeine in chocolate increases renal lithium clearance through its diuretic effect, lowering serum lithium levels. A sudden change in chocolate or caffeine intake — especially abrupt cessation — can cause serum lithium to rise into the toxic range, while sudden additions can push levels sub-therapeutic.