What is a primary risk associated with peptide hormones?

The correct option is associated with the fact that peptide hormones can influence the viscosity of the blood. When these hormones are administered or manipulated, they can lead to changes in various metabolic processes, including fluid retention and alterations in blood composition. This can result in the blood becoming thicker, which increases the risk of cardiovascular issues such as hypertension and the potential for clots.

In contrast, the other options do not typically reflect the primary risks linked to peptide hormones. Increased muscle fatigue, heightened immune response, and low energy levels can be symptoms or secondary effects related to a variety of factors in exercise or health contexts, but they are not direct risks associated specifically with peptide hormones. Therefore, understanding the effects of peptide hormones on blood viscosity and cardiovascular health is crucial when considering their use and the risks involved.