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Colonic bacteria can convert daidzein to equol, which has the same level of estrogenic activity as genistein and can absorbed.  Because of this, taking antibiotics during soy consumption could decrease overall estrogenicity of soyfoods.  Soy protein may interfere with warfarin's INR International Normalized Ratio for clotting time (after consuming 16 oz soymilk per day for 4 weeks), which returned to baseline two weeks after discontinuing soy milk.  Soy is unusually high in vitamin K which interferes with warfarin's mechanism of action and can affect INRs.  Tamoxifen may be abrogated or enhanced in conjunction with isoflavones in a dose-dependent manner; lower doses tend to interfere, higher doses may enhance effect.  Cisplatin's effects are potentiated by genistein addition to treatment.  Infants with congenital hypothyroidism required more levothyroxine replacement therapy while on soy formula, and adults required higher doses of levothyroxine for adequate thyroid hormone replacement in adult hypothyroidism.