In context of thyroid disorders, what does hypothyroidism primarily cause?

Hypothyroidism primarily causes a decreased metabolic rate. The thyroid gland produces hormones that are crucial for regulating the body's metabolism; when the production of these hormones is insufficient, the body's metabolic processes slow down. This reduction in metabolic activity can lead to a variety of symptoms including fatigue, weight gain, and sensitivity to cold, as the body is not burning energy efficiently.

It is important to understand the role of thyroid hormones—namely thyroxine (T4) and triiodothyronine (T3)—which are responsible for increasing the metabolic rate of tissues. In hypothyroidism, inadequate levels of these hormones result in diminished energy expenditure and slower physiology, thus confirming the characteristic of an overall decreased metabolic rate.