Are cough suppressants effective?

Despite what the "other" side seems to think, Skeptical bloggers are not in the pockets of Big Pharma. In that vein, this article will discuss over-the-counter (OTC) cough suppressants and whether or not they are efficacious.

Overview

When I was a kid, we would often get a spoonful of "cough syrup", but these days it seems that cough medicine is usually sold as part of a multi-symptom product such as Nyquil, Robitussin, or Dimetapp (and their store-brand equivalents). When speaking about cough suppressants for a dry cough, you take an antitussive, generally either dextromethorphan (The "DM" on the label of products) or codeine. For a productive cough, people will use an expectorant such as guaifensein.DM, which was approved for OTC usage in 1958, as a non-sedative alternative to codeine. But what about proof of efficacy?

Systematic reviews

There have only been a couple major systematic reviews of the scattering of studies about cough suppressants. A 2008 Cochrane Review of cough suppressants in an ambulatory setting (basically, at some sort of medical facility), encompassing about 3400 people (both adults and children), found "there is no good evidence for or against the effectiveness of OTC medicines in acute cough" (1). Some of the individual studies had positive effects, many were negative, which is sort of what is expected of anything without a strong effect or close to a placebo. A 2006 review article published in CHEST magazine also found "Peripheral and central antitussive agents can be useful in patients with chronic bronchitis, but can have little efficacy in patients with cough due to upper respiratory infection." (5)

There do not appear to be any systematic reviews specific to codeine (the Cochrane review above covers both). In a 1997 study that compared codeine to placebo, it was found that "codeine is no more effective than placebo in reducing cough associated with acute URTI". The authors also noted that while codeine is considered the "gold standard" against which other antitussives are measured, nobody had really looked at how effective codeine actually was in real world settings (4).

A 2005 study published in Psychosomatic medicinelooked directly at the effects of placebo (vitamin E) on cough and "placebo treatment has significant antitussive activity. This placebo effect may be related to generation of central neurotransmitters such as endogenous opioids" (6).

Even when looking at a "productive" cough (such as from bronchitis), the 2006 CHEST study above found that"mucolytic agents [such as guaifensein]are not consistently effective in ameliorating cough in patients with bronchitis, although they may be of benefit to this population in other ways."

Brian actually did aSkeptoid on placebos in 2009which references one of the review articles by Schroeder based on their 2002 research. It covers the placebo aspect much more.

Use in children

As a father, I know that while I might have no problem dealing with a cough, there is a strong desire to relieve discomfort for children so that they -- and, therefore, us -- can sleep better. The number of products you can give to children is very limited even to start with (mostly having to do with the risks of the clinical testing, similar to testing of things in pregnant women).

An overview of different types of cough in children and their treatments published in the Medical Journal of Australia found "there is little evidence for using medications for symptomatic relief of cough", citing an earlier version of the Cochrane review above (2).

The Archives of Pediatrics and Adolescent Medicine published a -- note: a single study, not a systematic review --study that found honeyto be more effective than a DM-containing product for "sleep quality" and treatment of cough. However, this was based on simply asking parents for their evaluation of the effectiveness. The results seem consistent with the antitussive effects of a placebo that the 2005 study identified (3).

Conclusion

So the short answer to the title of this post is "Yes, cough suppressants do something". The long answer is that OTC cough suppressants don't appear to do anything better than a placebo for coughing caused by upper respiratory tract infections (URTI). Neither codeine (which you almost certainly won't find in an OTC preparation), nor its more generally available alternative dextromethorphan (DM) appear to have any real effect above that of a placebo in over-the-counter dosages. Given that, in this case you may as well give children a spoonful of honey (my wife and I make "tea" out of hot water and honey)... at least it tastes good and it'll apparently work a bit. Note that honey should not be given to infants under a year or so due to risk of botulism.Based on the Skeptoid article on placebos, this topic seems like a great candidate for the "belief" that the remedy will work adding to the placebo effect.

UPDATE: 1/6/2012 Added note about botulism in honey and slight re-wording of conclusion to clarify that the results are for over-the-counter dosages of URTI, thanks to heads up from fellow Skeptoid writer (and actual medical practitioner), Stephen Propatier.

References

1. Smith, S. M., K. Schroeder, and T. Fahey. "Over-the-counter (OTC) medications for acute cough in children and adults in ambulatory settings." Cochrane Database of Systematic Reviews 9 (2008).

2. Chang, Anne B., Lou I. Landau, Peter P. Van Asperen, Nicholas J. Glasgow, Colin F. Robertson, Julie M. Marchant, and Craig M. Mellis. "Cough in children: definitions and clinical evaluation." Med J Aust 184, no. 8 (2006): 398-403.

3. Paul, Ian M., Jessica Beiler, Amyee McMonagle, Michele L. Shaffer, Laura Duda, and Cheston M. Berlin Jr. "Effect of honey, dextromethorphan, and no treatment on nocturnal cough and sleep quality for coughing children and their parents." Archives of pediatrics & adolescent medicine 161, no. 12 (2007): 1140.

4. Freestone, C., and R. Eccles. "Assessment of the antitussive efficacy of codeine in cough associated with common cold." Journal of pharmacy and pharmacology 49, no. 10 (1997): 1045-1049.

5. Bolser, Donald C. "Cough Suppressant and Pharmacologic Protussive Therapy ACCP Evidence-Based Clinical Practice Guidelines." CHEST Journal 129, no. 1_suppl (2006): 238S-249S.

6. Lee, Patrick CL, Mutaz SM Jawad, J. David Hull, Will HL West, Kerry Shaw, and Ron Eccles. "The antitussive effect of placebo treatment on cough associated with acute upper respiratory infection." Psychosomatic medicine 67, no. 2 (2005): 314-317.