**Core Concept**
The question tests the understanding of the pharmacological effects of inhaled corticosteroids, specifically the dose at which systemic adverse effects become evident. Inhaled corticosteroids are a cornerstone in the management of asthma and chronic obstructive pulmonary disease (COPD), acting locally in the lungs to reduce inflammation. However, at higher doses, systemic absorption can lead to adverse effects similar to those seen with oral corticosteroids.

**Why the Correct Answer is Right**
Systemic adverse effects of inhaled steroids, such as suppression of the hypothalamic-pituitary-adrenal axis, osteoporosis, and cataracts, are generally seen at higher doses. The exact dose at which these effects become significant can vary depending on the specific inhaled corticosteroid used, the patient's sensitivity, and the duration of treatment. Typically, doses above 500-1000 mcg per day of beclomethasone equivalent are associated with a higher risk of systemic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Doses less than this threshold are generally considered safe for long-term use without significant systemic effects.
**Option B:** This is too low, as many patients can tolerate this dose without systemic effects.
**Option D:** This is higher than necessary for the question's context.

**Clinical Pearl / High-Yield Fact**
It's crucial to monitor patients on high-dose inhaled corticosteroids for signs of systemic corticosteroid effects, including monitoring bone density and eye exams for cataracts. The goal is to use the lowest effective dose to control symptoms and minimize side effects.

**Correct Answer:** C. 1000 mcg.