Phenylephrine helps shrink the blood vessels in the nasal passage, reducing the stuffy nose. Cetirizine is an antihistamine that alleviates allergy symptoms by blocking histamine. Ambroxol works by thinning and loosening phlegm (mucus) in the lungs, windpipe, and nose and thus helps to cough out phlegm easily. Guaiphenesin increases the volume of fluid in the airways and helps to remove it from the airways. Paracetamol inhibits the production of prostaglandins (chemical messengers) in the brain responsible for pain and fever. Together, this combination helps to provide relief from cough.