The activity of the thyroid gland is apparently controlled by the hormone that comes from the pituitary gland. For a variety of reasons, the thyroid gland may be inactive or excessively active. Inactivity of the thyroid may result in the condition called cretinism which is associated with a deficiency of the thyroid gland in early childhood, and the condition called myxedema which comes on later in life. The person with myxedema has a typical face with puffy eyelids, and an apparent lack of interest in what is going on. The skin is dry and rough, the hair coarse, brittle and dry. Because the tongue and throat are swollen, the speech is slow and slurred. With this there is a tendency to slowing of all of the functions of the body and, because of the deficiencies of the blood and the circulation, the person with myxedema is sensitive to cold.
Since the condition is so certainly due to a lack of thyroid material, the treatment includes the giving of thyroid, and the dosage is adjusted according to the need of the patient and his response to the drug. Customarily doctors will begin with exceedingly small doses, because the thyroid is a potent material and overdosage may result in a rapid heart, sweating, loss of weight, and diarrhea. The maximum effect from any dose is not apparent until seven to ten days after the use of the drug is first begun, and the action will persist for one to three weeks after the drug is discontinued. The dosage of thyroid needs to be taken only once a day since, usually, nothing is gained, by dividing it over the day.