Warfarin: Patient Guide to Blood Thinning
Warfarin is an anticoagulant, or “blood thinner,” that reduces the risk of dangerous blood clots. It is used to treat or prevent clots, including those linked to deep vein thrombosis, pulmonary embolism, atrial fibrillation, and certain heart valve conditions. Your dose is adjusted using regular blood tests called INR measurements.
Warfarin can prevent serious clots, but it can also cause bleeding, so taking the correct dose and keeping regular INR appointments is essential. Never start, stop, or change your dose without guidance from your doctor or pharmacist.
Key facts at a glance
- ATC
- B01AA03
- Generic
- Warfarin
- Class
- anticoagulant
- Brands
- Coumadin, Jantoven
- Availability
- rx
- Pregnancy
- X
- Lactation
- caution
- Half-life (h)
- 40
- Routes
- oral
- Forms
- tablet
- Regions
- CN, US, EU, JP
- Monitoring
- coagulation, inr, dietary-vitamin-k
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Dosage and administration
- Usual dose
- 2-5mg once daily initially, maintenance 2-10mg once daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 0.1-0.2 mg/kg once daily initially, adjusted based on INR
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 1-3mg once daily initially, adjusted based on INR
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
Overdose information
Special Populations
8 groupspregnancy
first trimesteravoid use
warfarin is contraindicated in first trimester due to risk of embryopathy including nasal hypoplasia, stippled epiphyses, and central nervous system abnormalities
fetal ultrasound monitoring for anomalies
Use of this medication in this population requires careful consideration of risks and benefits.
pregnancy
third trimesteravoid if possible
use only if benefits outweigh risks; consider switching to heparin
close fetal monitoring
Use of this medication in this population requires careful consideration of risks and benefits.
lactation
breastfeedingno adjustment needed
warfarin is considered compatible with breastfeeding; minimal excretion in breast milk
routine infant follow-up
geriatric
elderlystart at lower dose
initiate therapy at lower doses (e.g., 2-3mg) and monitor INR closely; increased sensitivity to anticoagulant effects
frequent INR monitoring, assess for falls and bleeding
Use with caution and monitor for adverse effects.
pediatric_age
neonates and childrenweight-based dosing with frequent adjustments
requires individualized dosing; vitamin K supplementation may be needed; venous access considerations
frequent INR monitoring (often twice weekly during initiation)
Use with caution and monitor for adverse effects.
renal_impairment
all stagesno major dose reduction needed initially
warfarin is not renally excreted significantly; use standard initial dosing but monitor closely
regular INR monitoring; assess renal function periodically
Use with caution and monitor for adverse effects.
hepatic_impairment
mild to moderatereduce dose initially
liver disease impairs synthesis of clotting factors and warfarin metabolism; start with lower dose
frequent INR monitoring; monitor liver function tests
Use with caution and monitor for adverse effects.
hepatic_impairment
severeavoid or use extreme caution
severely impaired liver function markedly alters warfarin metabolism and clotting factor synthesis
intensive monitoring if used
Use of this medication in this population requires careful consideration of risks and benefits.
Statistics and clinical data
FDA approval year
Year warfarin was first approved for medical use in the United States
Drug class
Warfarin belongs to the anticoagulant class of medications
Common uses
Primary therapeutic applications of warfarin therapy
Mechanism of action
How warfarin works to prevent blood clot formation
Contraindications
Conditions and patient states where this medication should be avoided or used with caution.
Do not use (1)
Known allergy to this medication or its components
Use caution (1)
Consult healthcare provider for benefits vs risks assessment
Official drug label
WellAlly may earn a referral fee from linked resources at no extra cost to you. Editorial content is never influenced by commercial relationships.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed July 22, 2026. · Read our editorial policy