Herbal Medicine for Cough: a Systematic Review and Meta-Analysis.

Background: The aim of this review was to systematically assess the literature on herbal medicine for cough as a symptom of upper respiratory tract infections and common cold.

Methods: The Cochrane Library, Scopus, MEDLINE/PubMed, and Embase were searched through March 2012 for RCTs testing the effects of herbal medicine for cough. Risk of bias was assessed using the Cochrane tool.

Results: 34 RCTs (N = 7,083) on Pelargonium sidoides (11 RCTs), Echinacea (8 RCTs), Andrographis paniculata (6 RCTs), ivy/primrose/thyme (4 RCTs), essential oils (4 RCTs) and bakumondoto (1 RCT) were included. Controls were mainly placebo. Most studies had a low risk of bias. The meta-analysis revealed strong evidence for A. paniculata (SMD = -1.00, 95% CI = -1.85, -0.15; P<0.001) and ivy/primrose/thyme (RR = 1.40, 95% CI = 1.23, 1.60; P<0.001) in treating cough; moderate evidence for P. sidiodes (RR = 4.60; 95% CI = 2.89,7.31; P<0.001), and limited evidence for Echinacea (SMD = -0.68; 95% CI = -1.32, -0.04; P = 0.04).

Conclusion: This review found strong evidence for A. paniculata and ivy/primrose/thyme-based preparations and moderate evidence for P. sidoides being significantly superior to placebo in alleviating the frequency and severity of patients' cough symptoms. Additional research, including other herbal treatments, is needed in this area.