Which symptom is associated with hypothyroidism?

Weight gain is a classic symptom associated with hypothyroidism due to the slowed metabolism that occurs when the thyroid hormone levels are low. In hypothyroidism, the body's metabolic rate decreases, which often results in the accumulation of weight despite normal or even reduced caloric intake. The thyroid hormones play a crucial role in regulating metabolism, and a deficiency can lead to an energy imbalance where energy expenditure is not sufficient to offset caloric intake.

Other symptoms of hypothyroidism may include fatigue, depression, cold intolerance, and dry skin. While insomnia, tachycardia, and heat intolerance are more typically associated with hyperthyroidism, weight gain clearly points to the reduced metabolic activity observed in hypothyroidism, making it the most fitting choice in this context.