Antihistamines block the effect of histamine at histamine H1 receptor sites. Although they do not bind to or inactivate histamine, antihistamines ameliorate many of the effects of histamine excess (sneezing, itching and coughing/congestion). Some antihistamines are also used as sedatives/hypnotics or antiemetics. Mast cell stabilizers decrease the release of substances capable of initiating allergic reactions from mast cells. They are best used preventively. Decongestants usually have vasoconstrictor properties which decrease nasal congestion and have a drying effect. Ipratropium dries secretions via its anticholergic properties. Antitussives decrease cough by either a local anesthetic property ( benzonatate ) or by centrally inhibiting the cough reflex (opioid analgesics). Expectorants help to mobilize secretions. Cortiocosteroids decrease may symptoms of allergy via anti-inflammatory effects, either locally (nasal, inhalation, topical) or systemically.