Patients with some types of cardiovascular disease are prescribed anticoagulation therapy with Warfarin in order to control the ability of blood clotting. This work presents a co-designed mobile application, called Warfarin Guide, for a computer-assisted anticoagulant therapy. The application addresses the challenges that unexperienced patients may find when having to remember to regularly check their INR values and make temporary adjustments for INR value fluctuations that are not easy to interpret without direct medical advice.