**Core Concept**
Adrenal steroid therapy, also known as corticosteroid therapy, involves the administration of synthetic or natural corticosteroids to treat various inflammatory and autoimmune conditions. Absolute contraindications to adrenal steroid therapy are conditions where the benefits of therapy do not outweigh the risks.

**Why the Correct Answer is Right**
The correct answer is based on the understanding that adrenal steroid therapy suppresses the hypothalamic-pituitary-adrenal (HPA) axis, leading to adrenal insufficiency. Therefore, administering adrenal steroids to patients with adrenal insufficiency can exacerbate their condition, making it an absolute contraindication. This is due to the fact that patients with adrenal insufficiency have a pre-existing deficiency in cortisol production, and introducing exogenous steroids can further suppress the HPA axis, worsening the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while chronic use of adrenal steroids can lead to osteoporosis, it is not an absolute contraindication to therapy. Osteoporosis can be managed with appropriate treatment, and the benefits of adrenal steroid therapy may still outweigh the risks in certain cases.

**Option B:** This option is incorrect because while adrenal steroid therapy can cause hypertension, it is not an absolute contraindication. Hypertension can be managed with antihypertensive medications, and the decision to use adrenal steroids should be based on the individual patient's needs and risks.

**Option C:** This option is incorrect because while adrenal steroid therapy can cause mood changes, it is not an absolute contraindication. Mood changes can be managed with psychiatric support, and the benefits of adrenal steroid therapy may still outweigh the risks in certain cases.

**Clinical Pearl / High-Yield Fact**
When considering adrenal steroid therapy, it is essential to weigh the benefits against the risks and to carefully assess the patient's medical history, including any pre-existing conditions that may be exacerbated by therapy. A thorough discussion with the patient and their family is crucial to ensure informed consent and optimal management.

**Correct Answer:** C. Adrenal insufficiency.