Black Tea and Warfarin

Publication Date: 
Sun, 02/01/2015
By: Alere Staff

Black tea is also known as black leaf tea and English Tea. Patients drink black tea to improve mental alertness and cognitive performance. Prevention of Parkinson's disease and reducing the risk of some cancers have also been thought to be possible benefits of black tea.1

Interactions with Warfarin?

Black tea contains caffeine and as a result stimulates the central nervous system, heart muscle and possibly impact blood pressure.

Black tea's caffeine content may be associated with a competitive effect on platelet function. Caffeine may increase the risk of bleeding when used with warfarin, aspirin, clopidogrel, dipyridamole and ticlopidine. Increases in INR are theoretically possible but significant, consistent interactions have not been documented in humans.2


  1. Ascherio A, Zhang SM, Hernan MA, et al. Prospective study of caffeine intake and risk of Parkinson's disease in men and women. Proceedings 125th Ann Mtg Am Neurological Assn. Boston, MA: 2000; Oct 15-18:42 (abstract 53).
  2. Parker D, Hoffmann T, Tucker M, Meier D. Interaction Between Warfarin and Black Tea. Ann Pharmacother January 2009 vol. 43 no. 1 150-151.