Carbocisteine works by breaking down the mucus that is produced in the lungs. This helps to make the mucus less thick and sticky, so it is easier to cough up. Carbocisteine can be used to help make mucus less sticky in respiratory tract problems such as bronchitis, chronic obstructive pulmonary disease or cystic fibrosis. Mucus produced in the lungs is also known as sputum or phlegm. What is it used for? Making sputum (phlegm) easier to cough up in certain lung conditions, such as those listed below. Chronic obstructive pulmonary disease (COPD). Bronchitis. Cystic fibrosis.