Updated 25 July 2019

Ever wondered how cough syrups work?

Sponsored: The active ingredients in a cough syrup are specifically targeted to relieve the symptoms of a cough. Here's what you should know.

Coughing is annoying – both for you and the people around you – and the first thing you'll probably do is grab a bottle of cough syrup.

But have you ever wondered how a cough syrup works?

It's quite simple actually – the active ingredients in cough syrups are specifically targeted to relieve the symptoms of a cough. 

How the active ingredients work

Although there are a number of different active ingredients used in Benylin cough syrups, let’s take a look at two of the more common ones to better understand how cough syrups work.

Guaifenesin is an expectorant that helps loosen the phlegm and mucus caused by a wet cough, while dextromethorphan is a cough suppressant that can help relieve the symptoms of a dry, hacking cough.1

Without guaifenesin2, the mucus or phlegm that builds up in your chest and throat will remain thick and difficult to clear. Using a cough syrup with guaifenesin will, however, help loosen the mucus or phlegm, making it easier to clear it from your airways. 

Dextromethorphan1 suppresses the urge to cough. Think of the way a pair of sunglasses works – dextromethorphan works in a similar way2.

When you aren't wearing sunglasses, your eyes are exposed to the full glare of the sun's rays, making you unable to control the urge to squint.

The same applies when you have a cough – you want to stop or block that involuntary reflex to cough. Using a cough syrup with dextromethorphan will help reduce your urge to cough. 

Here are some questions3 to ask your doctor about your cough: 

  • Should I be worried that my cough won't go away?
  • Is my cough contagious?
  • Can I take antibiotics to get rid of my cough?
  • Could my cough be related to smoking?
  • Could my cough be related to allergies? 

 1. Michigan Medicine University of Michigan.[Internet]. Dextromethorphan and guaifenesin. University of Michigan.[updated 11 February 2018; Cited 2019/7/10. Available from
2. Johnson and Johnson Global HCP Cough Toolkit. Page 15 and 16.2018
3.[Internet] Cough Medicine: Understanding Your OTC Options. [updated 22 April 2019; Cited 2019/7/10.Available from 


Ask the Expert

Cough Expert

Professor Keertan Dheda has received several prestigious awards including the 2014 Oppenheimer Award, and has published over 160 peer-reviewed papers and holds 3 patents related to new TB diagnostic or infection control technologies. He serves on the editorial board of the journals PLoS One, the International Journal of Tuberculosis and Lung Disease, American Journal of Respiratory and Critical Medicine, Lancet Respiratory Diseases and Nature Scientific Reports, amongst others. Read his full biography at the University of Cape Town Lung Institute.

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