NHS Evidence Health Information Resources formerly National Library for Health

Non-prescription cough medicines 'could be a waste of money', reported the Daily Telegraph (23 January 2008). The newspaper was accurate in its reporting of a well-conducted review that appropriately concluded that there was no evidence for or against the effectiveness of over-the-counter medicines due to the lack of good quality trials.

The Daily Telegraph (1) reported that studies of non-prescription cough medicines showed little or no benefit in adults and children with coughs.
The newspaper article was based on findings from a well-conducted systematic review (2) carried out and published by the Cochrane Collaboration, and annotations made by one of the authors. The review included 25 relevant randomised controlled trials (RCTs), involving a total of 3,492 adults and children. Many of the trials were of poor quality and reported conflicting results. The review concluded that there was little evidence for the effectiveness of over-the-counter preparations for acute cough, and, given the paucity of good quality studies, the authors say the results of their review have to be interpreted with caution.
The newspaper was generally accurate in its reporting of the systematic review, the conclusions of which appear appropriate. A quote in the newspaper by one of the researchers that the absence of evidence should not be understood as 'evidence of no benefit' was emphasised. The suggestion that pain relief (paracetamol or ibuprofen) and natural remedies may be more effective than common over-the-counter medicines was a recommendation made by one of the authors based on personal experience; these were not medicines evaluated in the review.

Evaluation of the evidence base for the effectiveness of non-prescription cough medicines

Where does the evidence come from?

The systematic review was conducted by the Cochrane Acute Respiratory Infections Group. Funding was provided by the South & West Research and Development Directorate UK, the NHS Primary Care Career Scientist Fund UK, the Division of Primary Health Care, University of Bristol, UK and the Medical Benefits Fund of Australia.

What were the authors' objectives?

To assess the effects of oral over-the-counter cough preparations for acute cough.

What was the nature of the evidence?

The research, published as a Cochrane Review on the Cochrane Library, was a systematic review of 25 RCT's (17 in adults and 8 in children) involving 3,492 people (2,876 adults and 616 children). The authors searched a number of relevant databases and attempts were also made to locate additional studies by screening reference lists of articles and by contacting authors and cough medicine manufacturers. Only three studies were conducted outside Europe or the USA. Studies were grouped according to the type of drug evaluated, and the results for adults and children presented separately. Outcomes assessed included cough frequency, severity, and relief, sputum thickness and adverse effects of the treatments.

What interventions were examined in the research?

The review examined studies that evaluated the effect of oral antitussives, mucolytics, antihistamine-decongestant combinations, antihistamines and other combinations of drugs in both adults and children. Studies of the effect of expectorants in adults but not children were evaluated.

What were the findings?

Studies in adults: In studies of antitussives, expectorants and antihistamine-decongestant combinations conflicting results were found. One study investigating a mucolytic drug and three studies of other drug combinations reported a beneficial treatment effect. In three studies of antihistamines the treatment was no more effective than placebo.

Studies in children: In studies of antitussives, antihistamines, antihistamine decongestants, antitussive/ bronchodilator combinations the treatment was reported to be no more effective than placebo. The results of one trial were in favour of a mucolytic treatment. Of the two studies evaluating paediatric cough syrups, one indicated a beneficial effect and the other no effect.

Many studies failed to report adverse events. In some, generally mild adverse events were reported. The overall quality of the included studies was considered to be poor.

What were the authors' conclusions?

No good evidence is available for or against the effectiveness of over-the-counter medicines. Often results were conflicting and uncertain regarding their clinical relevance, and the results of the review have to be interpreted with caution.

How reliable are the conclusions?

This was a well conducted and reported systematic review, using the methods proposed by the Cochrane Collaboration. The authors addressed a clear research question defined in terms of study design, participants, intervention and outcomes. The authors searched several relevant databases. The study selection and data extraction processes were conducted in duplicate, and were therefore appropriate. The quality assessment revealed limitations of the included studies which question the reliability of their findings. Although several studies indicated a beneficial effect of treatments in comparison with placebo, they all had methodological limitations, or lacked details of the methodology used, making the reliability of their results uncertain. Studies included in the review differed markedly in terms of study characteristics and study quality, and this was highlighted by the authors. The authors' conclusion about the unclear benefits of oral non-prescription cough medicines is likely to be reliable.

Systematic reviews

Information staff at CRD searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic.

No additional systematic reviews were identified on the Cochrane Database of Systematic Reviews (CDSR), however there were two on the Database of Abstracts of Reviews of Effects (DARE) (3,4). The two papers identified on DARE are based on an earlier version of the Cochrane review.

References and resources

1. 'Don't waste money on shop cough remedies'. Daily Telegraph, 23 January 2008, p10.

2. Schroeder K, Fahey T. Over-the-counter medications for acute cough in children and adults in ambulatory settings. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD001831. DOI: 10.1002/14651858.CD001831.pub2.

3. Schroeder K, Fahey T. Should we advise parents to administer over the counter cough medicines for acute cough? Systematic review of randomised controlled trials. Archives of Disease in Childhood 2002;86:170-75. [DARE Abstract]

4. Schroeder K, Fahey T. Systematic review of randomised controlled trials of over the counter cough medicines for acute cough in adults. BMJ 2002;324:329-32. [DARE Abstract]