Hi johncamper,   Thank you for your question! I checked two references - one states there is no interaction between these medications, and the other states that the effect of these two medications taken together is unknown. I think the most important thing when taking both of these medications is to take them consistently. If you've been taking them 30 minutes apart and haven't had problems with your INR levels, then I would say you should continue taking it that way. Coumadin is very sensitive to change in diet, change in medication regimen, etc. If everything's okay right now with the way you're taking the Flomax, and your INR is where you want it to be, you should keep doing what you're doing.   Best of luck, Casey