FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam 2025 - Free NABP Practice Questions and Study Guide

Addison's disease is characterized by the underproduction of hormones by the adrenal glands, notably cortisol, which plays a crucial role in various bodily functions. Cortisol is a steroid hormone that helps regulate metabolism, the immune response, and stress response. In Addison's disease, the adrenal glands do not produce enough cortisol, leading to symptoms such as fatigue, weight loss, low blood pressure, and increased pigmentation of the skin.

The other hormones listed are not primarily relevant to Addison's disease. Insulin is produced by the pancreas and is responsible for glucose metabolism; its deficiency is associated with diabetes mellitus. Estrogen is primarily produced in the ovaries and is involved in the development of female secondary sexual characteristics and reproductive functions. Thyroxine, produced by the thyroid gland, is crucial for regulating metabolism and energy levels, but it is not the hormone that is deficient in Addison's disease. Therefore, the correct answer is indeed cortisol, as its deficiency is the hallmark of this condition.