Final answer:
The adverse effect of warfarin that the nurse should monitor for is excessive bleeding.
Step-by-step explanation:
The nurse should monitor for excessive bleeding as an adverse effect of warfarin. Warfarin is an anticoagulant medication that works by inhibiting the synthesis of clotting factors in the liver. While this is beneficial for preventing blood clots, it can also increase the risk of bleeding. The nurse should regularly assess the client for signs of bleeding, such as easy bruising, bleeding gums, blood in urine or stool, and prolonged or excessive bleeding from minor cuts or injuries.