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Sedating antihistamines for

Allergies occur when your immune system erroneously thinks an innocuous foreign substance, such as pollen or pet dander, is actually dangerous.

The newer, second-generation (ie, nonsedating) antihistamines are usually preferable to avoid sedation and other adverse effects associated with the older, first-generation antihistamines.

Ocular antihistamine drops (for eye symptoms), intranasal antihistamine sprays, intranasal cromolyn, intranasal anticholinergic sprays, and short courses of oral corticosteroids (reserved for severe, acute episodes only) may also provide relief.

Histamine is necessary to promote wakefulness, motivation and goal-directed behaviors; when the receptors for histamine are blocked, drowsiness occurs.

Many companies have marketed diphenhydramine and doxylamine (another sedating antihistamine) for insomnia under different brand names.

For example, when you're fighting a cold (the rhinovirus), histamines widen the blood vessels in your nasal cavity, causing nasal congestion.

Additionally, the increased fluid leakage from your blood vessels, combined with an increased mucous production — also caused by histamines — can result in a runny nose.

Older antihistamines, such as diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), and hydroxyzine (Atarax), also work well but have many side effects.