Nimesulide is a non-steroidal anti-inflammatory drug (NSAID). It works by blocking the release of certain chemical messengers that cause pain and inflammation (redness and swelling). Phenylephrine is a nasal decongestant which narrows the small blood vessels providing relief from congestion or stuffiness in the nose. Cetirizine is an antihistamine that alleviates allergy symptoms by blocking histamine. Caffeine is a central nervous system stimulant which works by blocking the action of certain natural substances (adenosine and phosphodiesterase). It can increase alertness and improve energy levels.