The medications used to treat allergies can cause a variety of behavioral symptoms. Different children react in very different ways to antihistamines, which are most often used to treat allergy symptoms. Some children become excitable, others depressed or drowsy. Some become irritable. Most have a shorter attention span, whether or not there are other symptoms.
Oral decongestants can cause restlessness and irritability, as can asthma medicines.
Many allergic children have trouble with sleep, either because of their symptoms or their medications. Even if antihistamines make them drowsy, they disturb the normal sleep cycles, resulting in daytime drowsiness or irritability. In some cases, allergic children may have enlarged adenoids or swolen membranes in the nose which causes obstruction to breathing at night. These children may have disturbed sleep, or may sleep longer than average. They are often irritable or drowsy during the day.