Warfarin is an oral ‘anticoagulant’, a medication taken by mouth to reduce the formation of blood clots.
It is prescribed for conditions such as some heartbeat irregularities, artificial heart valves, clotting in veins, heart attack or stroke. Too much warfarin may lead to serious bleeding, and too little will not prevent clotting. Warfarin must be taken exactly as prescribed and must be monitored with regular lab tests.
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Other sites:

http://www.warfarinfo.com/dvttherapy.htm

http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682277.html

http://health.yahoo.com/heart-prevention/warfarin/healthwise--d00022a1.html

http://bodyandhealth.canada.com/drug_info_details.asp?brand_name_id=1783

http://www.tigc.org/eguidelines/patient05.htm

http://www.tigc.org/eguidelines/warfarin05.htm

http://www.drugs.com/pdr/warfarin-sodium.html

http://patients.uptodate.com/topic.asp?file=blod_dis/6066

http://www.strokesurvivors.ca/index.php?nav=coumadin

http://www.drugdigest.org/DD/DVH/Uses/0,,705%7CWarfarin,00.html

http://www.medicinenet.com/warfarin-oral/article.htm

http://www.ptinr.com/data/pages/default.aspx?u=

http://www.askapatient.com/viewratings.asp?drug=9218&name=COUMADIN&sort=Timelength

http://www.clevelandclinic.org/health/health-info/docs/0800/0835.asp?index=4713

http://www.mybloodthinner.org/]http://www.mybloodthinner.org/

http://en.wikipedia.org/wiki/Warfarin

Mayo clinic