What happens when the thyroid gland is underactive?

Hypothyroidism: Low levels of thyroid hormone can result from a "sick" underproducing thyroid gland (thyroid disease) or a normal thyroid gland that is being under-stimulated by the pituitary gland; releasing sub-optimal amounts of thyroid stimulating hormones. Symptoms include weight gain, fatigue, hair loss, skin drying, constipation, as well as many other less common features.

Hypothyroid: Fatigue increased sensitivity to cold constipation dry skin unexplained weight gain puffy face hoarseness muscle weakness elevated blood cholesterol level muscle aches, tenderness and stiffness pain, stiffness or swelling in your joints heavier than normal or irregular menstrual periods thinning hair slowed heart rate depression.