In D3+K2 combinations, risk is largely driven by excessive vitamin D. Prolonged high doses can cause hypercalcemia, leading to nausea, constipation, fatigue, kidney stone risk, and in severe cases cardiac rhythm issues. Vitamin K2 is generally lower-toxicity but can interfere with warfarin, potentially altering anticoagulation control. Avoid using D3K2 products indiscriminately; set targets based on measured 25-OH vitamin D and consider monitoring calcium-related labs when appropriate, especially with kidney disease or disorders affecting calcium metabolism.