What side effects should I be expecting from taking warfarin?

Signs of warfarin allergic reactions: difficulty breathing, hives (rash on your body), swelling of the face, lips, tongue, or throat—If you experience any of these symptoms of an allergic reaction, please call 911 or seek emergency medical care at the nearest emergency room (ER). 

Warfarin is a blood thinner; thus, warfarin increases your risk of bleeding. These bleeding problems can be severe or even life-threatening. Call your doctor immediately if you have any signs of bleeding, such as:

• Bleeding gums that will not stop
• Severe nosebleeds
• Painful, excessive bruising with no known causes
• Severe bleeding after a minor injury
• Sudden, severe headache 
• Feeling weak or dizzy
• Blood in your urine 
• Bloody or tar-colored stools 
• Coughing up blood or vomit that looks like coffee grounds
• Bleeding from wounds or injection sites that will not stop
• Heavier than usual or abnormal vaginal bleeding

Call your doctor immediately if you experience any of the following signs:
Warfarin can cause necrosis or gangrene (death of cells or tissue caused by the block of blood flow); This is because the clots formed by warfarin may block the normal blood flow. If left untreated, amputation of the affected body part may occur as a result. Inform your healthcare provider and seek medical help immediately if you experience any of these symptoms:

• Skin changes or discoloration anywhere on your body
• Pain, swelling, hot or cold feeling of any body parts
• Sudden, severe leg or foot pain, foot ulcer
• Reddish, purple toes or fingers

Common side effects of warfarin:
The risk of bleeding is the most common side effect of warfarin. Other possible side effects include:

• Abdominal pain, gas, bloating
• Feeling cold or chills
• Slow-healing wounds 
• Change in the way things taste

The above list on this site may not include all the possible side effects of warfarin. Speak to your doctor or local pharmacist if you have persistent side effects or any that are not listed above. You can also report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088.

Warfarin Overdose: Go to the nearest emergency room or call the Poison Help Line at 1-800-222-1222. You can find more information at your local poison control center or at www.poisonhelp.org/help.

Symptoms of warfarin overdose: 
The primary concern with warfarin overdose is the risk of bleeding. Warfarin overdose can lead to excessive anticoagulation that can become life-threatening. Seek medical care immediately if you have any of the following symptoms as they can be signs of warfarin toxicity:

• Severe headache, dizziness
• Excessive bleeding after a minor injury
• Heavy bleeding during a monthly period or unusual bleeding for women
• Severe stomach pain or vomiting blood
• Pink, red, or dark brown urine
• Black, tarry, or bloody bowel movements

Source: FDA