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Acute cough is common and the demand for (and sale of) over-the-counter (OTC) cough medication is high, even for young children where serious side effects have been described.1 Keeping the evidence up-to-date is very important.
The authors searched CENTRAL, MEDLINE, EMBASE, CINAHL, LILACS, Web of Science and the UK Department of Health National Research Register for randomised controlled trials comparing oral OTC cough medications to placebo in adults and children. Six types of cough medicines were reviewed and included: antitussives, expectorants, mucolytics, antihistamine decongestant combinations, antihistamines and other combinations. The effectiveness of honey was also reviewed. Selected studies were independently reviewed by two authors. The risk of bias was assessed.
The authors included 29 trials, 19 in adults (3799 people) and 10 in children (1036 people). Of the 29 trials, 18 showed no difference between the cough medication and placebo. The data were not pooled due to the small number of studies for each category of medication, limited quantitative data and the heterogeneity of the studies. The authors concluded that the overall quality of the studies was poor, and there were conflicting conclusions. In adults, for example, four of the six studies of antitussives showed no difference between cough medication and placebo, while two studies showed decreased cough count compared to placebo (mean decrease of 19–36% in one study, p<0.05; mean decrease 12–17% in the other study, p=0.004). In children, antitussives, antihistamines, antihistamine–decongestants and antitussive/bronchodilator combinations were no different than placebo. One child study of a mucolytic demonstrated a mild improvement in symptom score compared to placebo (average difference 0.2 points on a 4-point scale, p<0.01). Children who received honey had significant improvements in symptom scores compared to placebo.
This is a well-performed and relevant systematic review which concludes that there is no good evidence for the effectiveness of commonly used OTC medicine to alleviate acute cough. The results are consistent with the previous versions of the review. It remains surprising that there exists so little scientific support for such commonly used medicines.
One limitation of the review is that herbal and homeopathic medicines were not included. These products are used frequently by patients with cough, and whether or not the remedies are effective and/or safe remains unanswered. It is possible that these products have not yet been studied in placebo-controlled trials which would have precluded their inclusion in the systematic review.
Another limitation is the overall low number of relevant studies. One can only guess why there are so few trials. A review on combination of oral antihistamine–decongestant–analgesic combinations for common cold was confronted with the same scarcity of evidence.3 Are possible financiers, such as pharmaceutical companies, afraid of negative results and dropping sales figures? The 20-year-old adage ‘the more common the less studied’ is obviously still very contemporary.4
Prior studies suggest that the most relevant outcome measure of effectiveness of cough medicine is subjective improvement as the therapy is meant as a purely symptomatic treatment. There is no sense in ‘objectively’ counting the number of coughs: it does not matter whether patients cough a few times less if they do not notice the difference. A prior study on severity reduction in the common cold found that ‘the smallest amount of patient-valued benefit that an intervention would require in order to justify associated costs, risk and other harms’ was about 25% improvement for a cheap treatment without adverse effects.2 When we look at the results not one single trial where a severity score was used seems to consistently reach this threshold, which suggests that cough medicines are not effective.
Implications for practice
For children, there is no evidence that cough medication helps and serious side effects can occur.1 The implication is unequivocal: we should not prescribe cough medication for children. In many countries this knowledge has reached national health organisations and regulations are strict. For example, in Belgium cough medication is contraindicated in children under 6 years and discouraged for children under 12 years. Honey maybe a safer alternative in children older than 1 year. In adults, effectiveness is also doubtful, but side effects are usually mild—although serious side effects have also been described.5 Doctors and pharmacists should explain to patients that acute cough is a self-limiting symptom and that at the moment they simply do not have an active medicine at their disposal.
Competing interests None.
Provenance and peer review Commissioned; internally peer reviewed.