Warfarin is a commonly used anticoagulant with documented reports of drug interactions. Tamoxifen is used in the adjuvant hormonal treatment of women with oestrogen-receptor- positive breast cancer. Warfarin and tamoxifen are known to interact with each other with a resultant increase in the bleeding tendency. These reports are mainly from the white population. We report a case of drug interaction between warfarin and tamoxifen with an acute onset. This report suggests that when these drugs are co administered, careful monitoring of the coagulation profile is needed.