Just as many foods, when combined, produce greater health benefits than each component does on its own, there are certain things that do not mix quite as well. According to the US Food and Drug Administration, two of these substances that refuse to get along are spinach and blood-thinning medication Warfarin.

The high levels of vitamin K found in spinach (as well as many other leafy green vegetables) has a clotting effect on on blood, rendering the drug far less effective. This blood thinner is usually prescribed to prevent clots typically associated with DVT (deep-vein thrombosis) -- also sometimes referred to as coach or business class syndrome, named for the section of an airplane that is often used by frequent air travelers.

If you happen to be taking a blood thinner of any kind, you may want to discuss any dietary restrictions with your doctor if you have not done so already.