Saturday, February 05, 2011

The big syrupy placebo effect.

Winter is here, and it's the time of year when coughs and colds are spreading alarmingly through the population. Fortunately our local pharmacies and supermarkets have their shelves well-stocked with remedies, not least those bottles of cough syrup to be taken by the spoonful in a reassuringly quaint manner, preferably while tucked up warmly in bed. I remembered hearing a little about the dubious efficacy of many cough medicine preparation so had a look at a Cochrane review on the subject. The Cochrane reviews provide a systematic search and analysis of the evidence available for a particular medication or practice, and look at both the results of trials and studies and the quality of the study and what exactly it was measuring. They're deservedly considered the gold standard in evidence-based medicine.

The drugs used in cough medicines can be divided into major group depending on their purported mode of action. Anti-tussives are cough suppressants, reducing the sensation of needing to cough, an appealing idea when you hav a dry irritating cough that keeps you awake. Expectorants are more or less the opposite, helping you to cough up the 'gunk' that builds up in your lungs and mucolytics work in a similar manner, thinning out the mucus and making it easier to shift. The final class is anti-histamines, often given together with decongestants.

The trials of anti-tussives show them to be remarkably useless, providing little or no improvement in symptoms compared to placebo, though it was interesting to see there was a significant reduction in symptoms seemingly due to the placebo effect, cough perhaps being a symptom particularly amenable to placebo for some reason? Anti-histamines and decongestants produced similar results. The expectorants and mucolytics appeared somewhat more promising, with some trials showing a statistically significant benefit compared to placebo, however the quality of trials giving such positive results was described as 'dubious', with flaws in both trial design and interpretation of data. The overall conclusion was that we have no reliable evidence that over-the-counter cough medicines in fact have any effect at all on cough symptoms. So what's that brightly coloured array of bottles and packages doing on our shelves, and what's actually in there?

The expectorant guaifenesin seems to be the usual active ingredient in the 'chesty cough' preparations. Dubious evidence being slightly better than none at all, it's reasonable to think this might be worth a try. But the best of all is the version for dry cough. A 'strong' version of most brands is available from pharmacies, containing a cough suppressant and a decongestant, which is...interesting when you the evidence . But if you think it's somewhat brazen to take people's money for a useless medicine, then look at the version you get on the supermarket shelves. Check the ingredient list, and it is exactly the same as the 'chesty cough' one, except without the active ingredient. So just the syrup base. This one is literally a big syrupy placebo. I guess the syrup might feel soothing if you have a sore throat from coughing, but would be very surprised if there was reason for it to be any more soothing than a spoonful of honey or syrup from your cupboard at home.

The packaging is also a thing to behold, robust red and royal blue for the ones that help you get up and get on with it, soft blues and lilacs for the ones that are supposed to help you sleep (though interestingly the mild anti-histamine sedative may be one of the few ingredients that does have a proven effect), consistent with the evidence that shows colour of a drug influences its effectivity. Graphics showing the flow of air through the bronchial and nasal passages, miraculously restored, images of the human body bathed in brilliant white healing light like a blessing, a warm golden glow focused at the site of the affliction. It's an absolutely fascinating study in advertising and the cultural and psychological connotations of 'medicine' as a concept, though it's difficult not to wonder whether if as much effort and money went into developing new products as into designing packaging and advertisments for the old ones, we might get more relief from our winter coughs.

But maybe not. Because perhaps the biggest flaw in these products: that they haven't been shown to work any better than placebo, is also their greatest strength: that they do work really quite well as placebos.