Study	Reason for exclusion
Abdul 1999	Adult study. Compared the antitussive effect of variations on dextromethorphan. No specific focus on cough types (i.e. chronic or non‐specific).
Eby 2006	Adult study. Assessed efficacy of zinc lozenges and zinc nasal sprays in controlling symptoms of the common cold. Zinc improved cold symptoms in 20% more of the participants, but there was no specific focus on coughs or chronic symptoms.
Fischer 2002	No focus on children. Assessed efficacy of ambroxol hydrochloride lozenges in acute uncomplicated sore throat relief.
Fujimori 1998	Adult study. Participants had chronic coughs of a specific nature (i.e. postinfectious), and were treated with variants of dextromethorphan to test the efficacies of the treatments.
Gilbert 2008	Report on Paul et al's 2007 study
Grattan 1995	Adult study. Compared inhaled and oral dextromethorphan in treating citric acid induced coughs.
Haidl 2001	Adult study on menthol efficacy in treating cough and dyspnoea. Those undergoing fibreoptic bronchoscopy were treated before, after, or with placebo, and the results showed no significant difference between the groups.
Lee 2000	Adult study. Assessed efficacy of dextromethorphan in treating acute upper respiratory tract infection.
Macknin 1998	Assessed efficacy of zinc gluconate lozenges in treating common cold symptoms in children, but no specific focus on coughs. The study found no benefit in treating with zinc lozenges in children and adolescents.
Matthys 1983	Adult study dealing with chronic stable coughs. Participants were treated with dextromethorphan or codeine and results compared, finding dextromethorphan to be a more suitable antitussive.
Mizoguchi 2007	No focus on children. Assessed efficacy of syrup containing paracetamol, dextromethorphan hydrobromide, doxyamine succinate, and ephedrine sulfate in treating symptoms of the common cold.
Mossad 1996	Adult study assessing the use of zinc gluconate lozenges for treating symptoms of the common cold. Results showed fewer days with coughing in lozenge‐treated group (2 days compared with 4.5 days in placebo group).
Paul 2004	Examined the use of dextromethorphan, diphenhydramine, and placebo in children with coughs related to upper respiratory tract infection.
Paul 2007	Studied the ability of honey to treat cough in children, including participants from 2‐18 years and comparing honey to dextromethorphan and no treatment. Coughs were due to acute viral respiratory infections. Those receiving honey showed greater improvements in cough severity and sleep disruption.
Prasad 2000	Adult study testing efficacy of zinc acetate lozenges in reducing duration and severity of symptoms of common cold. Lozenges were found to reduce duration and severity of cough in this study.
Prasad 2008	Adult study testing efficacy of zinc acetate lozenges in reducing duration and severity of symptoms of common cold. Found lozenges reduced duration of coughs.
Scavino 1985	No focus on children. Assessed efficacy of treating common cold symptoms with dextromethorphan hydrobromide syrup compared with placebo.
Schutz 2002	Adult study examining the local anaesthetic properties of ambroxol hydrochloride lozenges in the context of sore throat.
Taylor 1993	Evaluated treating acute night coughs in children with dextromethorphan, codeine, or placebo. Results showed that neither codeine nor dextromethorphan were superior to placebo in treating night cough in children.
Weippl 1984	Compared common cold symptom alleviation in children using a dextromethorphan‐based syrup (SCH 399) and an expectorant containing antihistamine. Treatment with SCH 399 was found to be more effective.
Yoder 2006	Assessed efficacy of dextromethorphan, diphenhydramine, and placebo in treating nocturnal cough in children due to acute upper respiratory tract infection.