Which finding indicates a complication of long-term prednisone therapy?

The correct answer, which indicates a complication of long-term prednisone therapy, is the presence of black, tarry stools. This finding suggests gastrointestinal (GI) bleeding, which is a serious side effect associated with corticosteroid use. Prednisone can increase the risk of peptic ulcers and gastrointestinal hemorrhage, especially when taken over an extended period. The anti-inflammatory properties of prednisone can mask symptoms of ulcers, making it crucial for patients on long-term therapy to be vigilant for signs of bleeding.

In contrast, while fatigue, insomnia, weight gain, fluid retention, and skin rashes or acne are known side effects of prednisone, they do not indicate the same level of urgency or potential harm as the possibility of GI bleeding. Therefore, the presence of black, tarry stools is a more direct indication of a severe complication linked to prolonged prednisone use.