Histalex 100 ml Syrup contains Chlorpheniramine Maleate, an antihistamine commonly used to treat symptoms of allergic conditions, including hay fever, urticaria (hives), rhinitis, and other allergic reactions such as sneezing, itching, and watery eyes. Chlorpheniramine works by blocking histamine receptors, which are responsible for triggering allergic symptoms. This syrup formulation is especially useful in treating common cold symptoms, mild allergic reactions, and motion sickness. It is usually taken in doses appropriate for age, typically 1–2 teaspoonfuls for children and adults, depending on the severity of symptoms. Common side effects may include drowsiness, dry mouth, and dizziness. As with any antihistamine, it is important to follow dosing instructions closely and consult a healthcare provider before use, especially for individuals with underlying medical conditions or those on other medications.