Well well well! I had to go for a blood test today and another woman said to the nurse that she had an awful cough and was going to get some cough medicine later. After the woman had gone, the nurse said 'a fat lot of good that will do her'! I asked why and she said that there is no evidence that cough medicines do anything - I was puzzled. So, I have just googled it and she's correct!
There is no good evidence from research studies that cough medicines work. It is thought that they have little benefit on the cough (or cold) symptoms.
www.patient.co.uk/health/cough-medicines
Web MD admits that: "The NHS says there's not much scientific evidence that cough medicines work … The NHS says there are no shortcuts with coughs caused by viral infections. It just takes time for your body to fight off the infection." Sure, if the syrup contains paracetamol, it might ease your aching head; if there's any antihistamine in there, your streaming nose and eyes might dry up a bit. If you want to soothe your throat, honey and lemon is at least as good – the Guardian's told you that already.
www.theguardian.com/commentisfree/2012/oct/16/cough-medicine-wont-cure-you
The WebMD link (there are 2 pages on this link) also states that we should be wary about which cough medicines we take as the ingredients may interfere with medications we already take or exacerbate an existing medical condition:
Many experts question the use of cough medicines because clinical trials have not found that cough medicines are any better than a placebo or dummy treatment.
If all that is true, how come big pharma can make the claim that these 'syrups' (as I shall now call them) help to get rid of a cough? Isn't that misleading? Have you seen the price of Benylin!