What is the primary use of antihistamines?

Antihistamines are primarily used to treat allergies and hypersensitive reactions because they work by blocking the action of histamine, a substance in the body that is involved in allergic responses. When the body encounters an allergen, histamine is released, leading to symptoms such as itching, sneezing, and runny nose. By inhibiting histamine's effects, antihistamines alleviate these symptoms, making them essential for individuals suffering from allergies, hay fever, or conditions like hives.

The other choices do not pertain to the primary use of antihistamines. While medications for treating anxiety disorders, managing blood pressure, and controlling diabetes are important, they serve different therapeutic purposes and mechanisms than antihistamines. Hence, option B accurately reflects the main function of antihistamines in medical practice.