How long does it take warfarin to work?

At least a few days. It can take up to 5 or more days for the medication to reach therapeutic effect. Sensitivity to the medication is based on genetic factors, as well as interaction with diet and other medications. Other newer anticoagulants may work within hours.
A couple of days or. So. As dr. Kaplan said, we generally expect that it will take 5 days for someone's level of Coumadin (warfarin) to be be what we call therapeutic. Coumadin (warfarin) starts to have home effect within 48 hours but it takes longer for Coumadin (warfarin) to reach a steady state level in you blood stream so we know what dose of it you should take long term (most of the time).