Which of the following symptoms is consistent with hypothyroidism?

Unexplained weight gain is a commonly recognized symptom of hypothyroidism, which occurs when the thyroid gland does not produce enough thyroid hormones. These hormones play a critical role in regulating metabolism, and a deficiency can lead to a slower metabolic rate. As a result, individuals may gain weight despite normal eating habits and physical activity levels.

In contrast, heat intolerance is often associated with hyperthyroidism, where an excess of thyroid hormones increases metabolism and contributes to feelings of being overheated. Constipation can occur with hypothyroidism, but it is a less definitive symptom when compared to weight gain. Hair loss can also be a symptom of hypothyroidism, but it is not as directly attributable as weight gain to the overall metabolic slowdown that defines the condition. Therefore, unexplained weight gain serves as a more direct and commonly acknowledged indicator of hypothyroidism.