Complex sentence: Decongestant nasal sprays are available over-the-counter in many countries, including: the United States, New Zealand, Ireland and the UK, work to very quickly open up nasal passages by constricting blood vessels in the lining of the nose.
Split into simpler sentences: Decongestant nasal sprays are available over-the-counter in many countries. They work to very quickly open up nasal passages by constricting blood vessels in the lining of the nose.