I believe you can drink grape juice on coumadin, (warfarin) but is it safe to drink welches 100% purple grape juice?

Probably: This question is often asked with regards to any food or drink. All you have to know is keep your diet consistent and follow-up for mandatory blood monitoring. If you decide to alter your diet, make sure that Vit K intake stays consistent otherwise your levels fluctuate. So, if you have been drinking it then yes it's fine. If you haven't, drink a small amount occasionally until level checked.

Yes: You can drink it in moderation. The key to maintaining your Coumadin (warfarin) levels is eating the same amounts of vitamin I containing products daily.

Grape juice: 100% purple grape juice should be just fine with coumadin (warfarin). The issue is how much vitamin K is in there, and it is fairly low. I always recommend my patients eat a healthy diet, and keep the amount of vitamin K steady day in and out so that their dosing of the coumadin (warfarin) can also be steady. Best wishes to you!