Efficacy and Safety of Eucalyptus for Relieving Cough: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

To assess the efficacy and safety of Eucalyptus globulus Labill (Eucalyptus) on cough. Cough is a common symptom of upper respiratory tract infections (URTIs) and bronchitis. Eucalyptus products are frequently used as over-the-counter cough medications but their efficacy and safety are uncertain. Randomized controlled trials (RCTs) investigating efficacy and safety of Eucalyptus for cough were systematically searched in electronic databases till February 2021. Two reviewers independently performed study selection, data extraction, and quality assessment. Clinical outcomes including improvement or resolution of overall cough symptoms, cough frequency (CF), and adverse events (AEs) of Eucalyptus were evaluated and analyzed using a random-effects model. Heterogeneity was evaluated using I and chi-squared test. Six RCTs with 1,857 participants with cough were included in this study. Most of the included studies used Eucalyptus in combination formula (four of six studies). Based on Cochrane's risk of bias criteria, three of six studies (50%) were rated low risk of bias, whereas the remaining were judged as high risk of bias. This study found that Eucalyptus products are more effective than placebo in terms of improvement or resolution of overall cough symptoms with relative risk 1.45 (95% confidence interval (95% CI) 1.26-1.67). Whereas all Eucalyptus formulae reduced CF with weighted mean difference 0.44 (95% CI 0.28-0.60), when compared with placebo. There are no serious AEs associated with Eucalyptus during treatment periods. Mild-to-moderate gastrointestinal symptoms were common AEs reported in a comparable study between Eucalyptus and control groups. The findings indicate that Eucalyptus products are safe for use in cough related to respiratory diseases such as URTIs and bronchitis. However, their efficacy is minimal and of uncertain clinical importance. Further high-quality studies are still necessary to confirm this finding.