Relieving congestion, cough, and throat and airway irritation due to colds, flu, or hay fever. It may also be used for other conditions as determined by your doctor. Zephrex is a decongestant and expectorant combination. It works by constricting blood vessels, reducing swelling in the nasal passages, and thinning and loosening mucus. This allows you to breathe more easily and makes coughs more productive.