Phenylephrine Hydrochloride is a decongestant that works by constricting blood vessels in the nasal passages, reducing swelling and congestion. It mimics the action of adrenaline on alpha-adrenergic receptors, offering quick relief from nasal blockage caused by colds, allergies, or sinusitis. It is often included in combination cold and flu remedies and is an alternative to pseudoephedrine with less potential for misuse.