Which of the following is NOT a symptom of Addison's disease?

In Addison's disease, the body fails to produce adequate amounts of hormones, particularly cortisol and aldosterone, from the adrenal glands. This hormonal deficiency leads to a range of specific symptoms, while weight gain is not typically associated with the condition.

Hyperpigmentation occurs due to increased production of adrenocorticotropic hormone (ACTH), which stimulates melanin production in the skin, causing dark patches. Hypotension, or low blood pressure, is a common symptom as a result of decreased aldosterone, which normally helps to regulate blood pressure and fluid balance. Hyponatremia, or low sodium levels in the blood, occurs due to a deficiency in aldosterone, which leads to sodium loss.

In contrast, weight gain is not a symptom of Addison's disease; instead, patients often experience weight loss and decreased appetite due to the inadequate hormone levels affecting metabolism and fluid regulation. This fundamental difference clarifies why weight gain does not fit the profile of symptoms for Addison's disease.