HTS code 2937.90.40.00 covers "Hormones, prostaglandins, thromboxanes and leukotrienes, natural or reproduced by synthesis; derivatives and structural analogues thereof, including chain modified polypeptides, used primarily as hormones › Other › l-Thyroxine (Levothyroxine), sodium" under the US Harmonized Tariff Schedule. This is the official duty rate charged by US Customs when this product is imported into the United States, sourced directly from the U.S. International Trade Commission and refreshed daily.