It's been 80 years and we still haven't figured out how to reliably perform loading doses (when someone is just starting out on warfarin) and to maintain stable INR (anticoagulation effectiveness, essentially) in people who take it daily. Lots of work has been done on it, but it is petering out due to the recent introduction of new anticoagulation drugs that do not require regular monitoring.

I happen to take warfarin daily, happy to answer any questions!