The document discusses various drugs used to treat symptoms of respiratory illnesses like the common cold. Antihistamines block the effects of histamine to reduce symptoms like runny nose and sneezing. Nasal decongestants constrict blood vessels in the nasal passages to relieve congestion. Antitussives suppress the cough reflex for nonproductive coughs. Expectorants thin mucus making it easier to cough up. Treatment is aimed at relieving symptoms rather than curing the underlying illness.