The only possible contraindication is the use of coumarin/warfarin derivatives as oral anticoagulants (OAC). These drugs are believed to be vitamin K antagonists and one has to be careful taking vitamin K supplements when taking vitamin K antagonists.
However the the story is not quite as simple as that. Reducing your vitamin K intake can cause your INR to increase and may make it more difficult to control. Rather than avoiding vitamin K, you should maintain a consistent intake of vitamin K by maintaining a consistent diet. In other words, from week to week, you should try to eat the same types of foods. For instance eating lots of leafy greens with high vitamin K one week and hardly the next is not conducive to your warfarin treatment.
Several recent studies, both in the US and Britain, have found that supplementing with low-dose vitamin K (50-150 mcg/day) may help stabilise the daily fluctuations in INR that occur due to varying dietary intakes of vitamin K. It has been shown that regular consumption of a modest amount of vitamin K actually helps stabilise the anticoagulant effects of warfarin. Vitamin K intake may thus help individuals using warfarin achieve the therapeutic benefits of the drug.
Obviously it is a very delicate balance and should be done in consultation with your doctor.
To be clear - we do not advocate start supplementing with vitamin K if on prescription medicine and especially if taking warfarin or other blood thinners. Vitamin K supplementation is an option which could actually help as long as it is done in the correct way and in correct balance. As such we highly recommend speaking to your doctor before using any supplement.