Which symptom is commonly associated with adrenal insufficiency?

Skin hyper-pigmentation is a symptom commonly associated with adrenal insufficiency, particularly in conditions such as Addison's disease. This arises from an increase in adrenocorticotropic hormone (ACTH) levels due to low cortisol production by the adrenal glands. The excess ACTH can stimulate melanocytes, the cells responsible for producing melanin, leading to darker skin patches, particularly in sun-exposed areas and on scars or mucous membranes.

In contrast, weight gain and increased blood pressure are typically not symptoms of adrenal insufficiency; they are more commonly associated with conditions like Cushing's syndrome, where there is an excess of cortisol. Thickening of hair is also not a primary symptom of adrenal insufficiency and doesn't correlate with the hormone levels involved in this condition. Therefore, skin hyper-pigmentation stands out as the hallmark symptom linked to adrenal insufficiency.