Which of the following is a contraindication for warfarin therapy?

Thrombocytopenia, which refers to a lower than normal number of platelets in the blood, is a contraindication for warfarin therapy because it increases the risk of bleeding complications. Warfarin is an anticoagulant that works by inhibiting the formation of blood clots, and if a patient already has a diminished capacity to form clots due to low platelet counts, the likelihood of serious bleeding events increases significantly.

While obesity, chronic headaches, and hypertension may have some relevance in the overall management of a patient on anticoagulant therapy, they do not inherently prevent the use of warfarin in the same way thrombocytopenia does. For example, obesity may require closer monitoring of the drug’s effects due to potential differences in pharmacokinetics, and chronic headaches or hypertension may necessitate adjustments in treatment but do not pose a direct contraindication to warfarin use. Therefore, the presence of thrombocytopenia is the most critical factor making it unsafe to initiate warfarin therapy in such patients.