Metabolised by CYP 1A2. Widely used as beverage but no reports of porphyrinogenic effects. One reference:

(To be edited, initial data ST OCT 04) Xantine derivative used as a stimulant and headache analgesic. Metabolized by CYP1A2. Inhibitor of CYP 1A2.

Uneventful use reported in 1 patient with acute porphyria.