Chocolate Interactions

Caffeine and theobromine from chocolate are competitive antagonists at A1 and A2A adenosine receptors. When intravenous adenosine or regadenoson is used for a cardiac stress test, or adenosine is used to terminate supraventricular tachycardia, recent methylxanthine intake can blunt the drug's effect and produce a falsely normal stress test or a failure to convert the arrhythmia.

Chocolate contains caffeine, a mild diuretic that increases how much lithium the kidneys clear. Because lithium has a narrow therapeutic window, a large, sustained change in caffeine intake can nudge serum lithium levels — adding a steady caffeine habit can lower them, while abruptly stopping one can raise them. Chocolate is a relatively minor caffeine source compared with coffee or tea, so the effect matters most for heavy, consistent chocolate consumers who make a sudden change.