Robitussin chesty cough with congestion symptoms of a chesty cough with congestion productive thick and sticky mucus or phlegm tightness in the chest blocked nose andor sinuses how robitussin works loosens and thins mucus or phlegm making it easier to cough up relieves nasal and sinus congestion soothes the chest area sugar free non drowsyas an alternative doctors can also prescribe medication that can assist with flu please visit our online doctor service to proceed with an influ