Antihistamines are indicated for which of the following conditions?

Antihistamines are primarily indicated for treating conditions related to allergies, such as nasal allergies and allergic reactions. They function by blocking the action of histamine, a substance in the body that is released during an allergic response. This helps alleviate symptoms like sneezing, itching, runny nose, and hives, making them particularly effective for individuals who suffer from allergic rhinitis or other allergy-related conditions.

In contrast, other options are less appropriate for antihistamine use. For example, while cough suppressants may be necessary in certain cases of cough, antihistamines do not target the underlying causes of a cough and may even thicken mucus in some situations. Headache relief typically involves pain relievers that target headache pathology, rather than an antihistamine, which does not address headache symptoms effectively. Similarly, chronic fatigue is often rooted in a range of factors that require a more comprehensive approach to treatment, rather than relying solely on antihistamines, which do not directly address fatigue symptoms.