BMJ Group Medical Reference
These are cough medicines that are supposed to help you bring up mucus from your airways. You can buy lots of different sorts from a pharmacist. They contain many different substances, such as guaifenesin, squill, and ammonium chloride.
Expectorants are often sold in cough and cold remedies, and come combined with painkillers and medicines called decongestants.
But there's very little research to say whether drugs which aim to clear mucus will help bronchitis. 
One study looked at a German herbal syrup made with thyme and ivy, called Bronchipret Saft.  The study found that people who took the syrup coughed less and had fewer symptoms than people who took a dummy (placebo) syrup. However, this is just one study and we need to see more research to be sure it works.
Many cough and cold remedies aren’t recommended for children under 2. If you're in any doubt whether a product is suitable, talk to your doctor or pharmacist. To find out more, read Treating coughs and colds in children.
A placebo is a 'pretend' or dummy treatment that contains no active substances. A placebo is often given to half the people taking part in medical research trials, for comparison with the 'real' treatment. It is made to look and taste identical to the drug treatment being tested, so that people in the studies do not know if they are getting the placebo or the 'real' treatment. Researchers often talk about the 'placebo effect'. This is where patients feel better after having a placebo treatment because they expect to feel better. Tests may indicate that they actually are better. In the same way, people can also get side effects after having a placebo treatment. Drug treatments can also have a 'placebo effect'. This is why, to get a true picture of how well a drug works, it is important to compare it against a placebo treatment.
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