EMJEF -- if you're taking 9 mg one day and 10 mg the next, your INR will vary slightly depending on the day that you test it. The swing will be a result of the varying dose coursing through your system.
Taking the same daily dose should make your INR reading more consistent, day to day.
The easiest way to do this is to get 7.5 mg of Warfarin, then add 2 mg (you can do this with two 1 mg pills, 1/2 of a 4 mg pill or, if available, one 2 mg pill).
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Grapefruit, and grapefruit juice interacts with many medications - and not just warfarin. Personally, I stay away from it - even in its dilute form.
Cranberry, and cranberry juice (and cranberry juice cocktail, cran-orange, cran-raspberry, cran-whatever) can also cause changes in your INR - especially if you have a lot of it.
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K2 has no impact on INR. You may want to check your bottles of K2 to be sure that they don't contain K2 AND K1. Sometimes they will.
I've been taking K2 plus D3 (in a single gel cap), or K2 by itself plus D3 capsules. The pure K2 hasn't had any effect on my INR.
It's K1 that can cause problems -- NOT K2
FWIW - Before I started to self-test, I had a blood draw, and my doctor called me, frantic, because my INR was 7. I just reduced my dosage and was careful not to injure myself for a few days.