Drugs that break up mucus
BMJ Group Medical Reference
This information is for people who have chronic obstructive pulmonary disease (COPD). It tells you about drugs to break up the mucus in your lungs, a treatment used for COPD. It is based on the best and most up-to-date research.
Do they work?
We're not certain. If you have the type of chronic obstructive pulmonary disease (COPD) called chronic bronchitis, drugs that break up the mucus in your lungs may help. But we need more research to be certain.
What are they?
Medicines that break up mucus are called mucolytic drugs, or mucolytics. They make the mucus in your lungs less sticky, so it's easier to cough out of your airways.
The National Institute for Health and Clinical Excellence (NICE) is the organisation that decides which treatments should be available on the NHS. NICE recommends that you should be prescribed mucolytic drugs if you have COPD and cough up a lot of mucus. 
Mucolytic drugs usually come as tablets that you take two to four times a day. In the UK, most doctors use mucolytics called carbocisteine and mecysteine (brand name Visclair). A new type, called erdosteine (Erdotin), can be used if you have a COPD attack (exacerbation). You take capsules twice a day, for up to 10 days. 
How can they help?
If you take a mucolytic drug, you may have slightly fewer attacks than if you don't take this kind of medicine.   An attack is when symptoms like breathlessness suddenly get worse.
You can also expect to have about six fewer 'sick days' each year (days off work or days when you can't do much because of your COPD). 
How do they work?
Mucolytic drugs make the mucus in your lungs thinner so that it's easier to cough up. If you have less mucus in your lungs, you are less likely to get chest infections that can make you feel sick and out of breath. Infections can also affect how well your lungs work, and cause a drop in how you score on lung function tests. See Spirometry for more information about these tests.
Can they be harmful?
Mucolytic drugs don't seem to cause many side effects. In studies, people were no more likely to get side effects from a mucolytic drug than from a dummy treatment (a placebo).