Desiccated thyroid or thyroid extract, refers to porcine (or mixed beef and pork) thyroid glands, dried and powdered for therapeutic use. Pork, or mixed beef and pork, thyroid preparations were developed in the late 1800s, and are still used today to treat hypothyroidism (underactive thyroid gland). This product is sometimes referred to as "natural thyroid", "natural thyroid hormones", "pork thyroid", thyroid USP, thyroid BP, or by the name of the best-known brand, "Armour thyroid".