Common side effects of Coumadin include bloating, mild stomach pain and gas, according to Drugs.com. Because Coumadin is a blood thinner, indications of unusual bleeding or bleeding that does not stop require immediate medical attention. An allergic reaction to Coumadin may present as an inability to breathe, facial swelling or hives.
The anticoagulant Coumadin, or warfarin, reduces the formation of blood clots in veins and arteries and is prescribed to help prevent strokes and heart attacks, explains Drugs.com. The presence of black or bloody stools or the coughing up or vomiting of blood may indicate internal bleeding in the stomach or intestines and requires immediate medical care. Severe reactions to Coumadin requiring immediate physician consultation include purple toes or fingers, severe pain or ulcers in the lower extremities, easy bruising, sudden dizziness or headaches, and jaundice.
Individuals taking Coumadin need to use extra caution when performing activities that can increase the risk of bleeding, such as shaving, or undergoing dental, medical or surgical procedures that might open the skin, notes Drugs.com. Over-the-counter pain relievers that affect blood clotting and interact negatively with Coumadin include aspirin, ibuprofen, acetaminophen and naproxen. Eating foods high in vitamin K, including some leafy green vegetables, vegetable oils and liver, can render Coumadin less effective, and combining grapefruit products with the medication can cause undesirable side effects. Coumadin users are advised to wear medical alert tags that indicate the presence of the drug in their systems.