Diphenhydramine is primarily used to treat which of the following symptoms?

Diphenhydramine is an antihistamine that is primarily used to alleviate symptoms associated with allergic reactions and the common cold. It works by blocking the action of histamine, a substance in the body that is responsible for many allergy symptoms. Therefore, its primary indications include relief from sneezing, itching, runny nose, and other symptoms related to allergies or the common cold.

Given the other choices, they do not align with the primary uses of diphenhydramine. High blood pressure and heart conditions are typically treated using different classes of medications, such as antihypertensives, rather than antihistamines. Medications to address fever and pain are usually analgesics or antipyretics, not antihistamines. Lastly, muscle pain and inflammation are generally treated with nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids, which are also distinct from the action of diphenhydramine. Therefore, C is the choice that accurately reflects the primary use of diphenhydramine.