Will it give me STD's or hard poop?
Although allergic reactions are possible, there is no known toxicity associated with high doses of phylloquinone (vitamin K1), or menaquinone (vitamin K2) forms of vitamin K.

The same is not true for menadione (vitamin K3) and its derivatives. Menadione can interfere with the function of glutathione, one of the body's natural antioxidants, resulting in oxidative damage to cell membranes. Menadione given by injection has induced liver toxicity, jaundice, and hemolytic anemia (due to the rupture of red blood cells) in infants, and is no longer used for treatment of vitamin K deficiency. The anticoagulant effect of vitamin K antagonists (e.g., warfarin) may be inhibited by very high dietary or supplemental vitamin K intake. It is generally recommended that individuals using warfarin try to consume the AI for vitamin K (90-120 mcg), while avoiding large fluctuations in vitamin K intake that might interfere with the adjustment of their anticoagulant dose.

Large doses of vitamin A and vitamin E have been found to antagonize vitamin K. Excess vitamin A appears to interfere with vitamin K absorption, while a form of vitamin E (tocopherol quinone) may inhibit vitamin K-dependent carboxylase enzymes.

Bleeding was reported in a man taking 5 mg of warfarin and 1,200 IU of vitamin E daily.

When given to pregnant women, warfarin, anticonvulsants, rifampin, and isoniazid can interfere with fetal vitamin K synthesis and place the newborn at increased risk of vitamin K deficiency.

Prolonged use of broad-spectrum antibiotics may decrease vitamin K synthesis by intestinal bacteria. Cephalosporins and salicylates may decrease vitamin K recycling by inhibiting vitamin K epoxide reductase. Cholestyramine, cholestipol, orlistat, mineral oil, and the fat substitute olestra may decrease vitamin K absorption.