Which medication is commonly used as a nasal decongestant?

Phenylephrine is widely recognized as a nasal decongestant due to its mechanism of action, which involves causing vasoconstriction in the nasal passages. By constricting the blood vessels in the nasal mucosa, it effectively reduces swelling and congestion, making it easier for individuals to breathe through the nose. This property makes it a popular choice in over-the-counter cold and allergy medications aimed at alleviating sinus and nasal congestion.

In contrast, the other medications listed serve different purposes. Dobutamine is primarily used as a cardiac stimulant in heart failure and shock management. Regitine, or phentolamine, is an alpha-adrenergic antagonist used to manage hypertension, particularly in pheochromocytoma. Labetalol is a beta-blocker that also has alpha-blocking properties, typically used to treat high blood pressure, but it is not indicated for nasal congestion. Thus, phenylephrine stands out as the correct answer in the context of nasal decongestion.