The key caution applies to people on warfarin or other vitamin K antagonist anticoagulants, as K2 can disrupt INR control. Those with clotting disorders, thrombosis history, or medications affecting coagulation should only use K2 under medical guidance. Pregnancy, breastfeeding, children, and severe liver/bile/gut absorption issues also call for individualized decisions. Avoid unrealistic expectations (“cleans arteries”); any benefit depends on context, biomarkers, and a personalized risk–benefit assessment.