Aims: To assess the efficacy of herb and plant extracts in the management of asthma.
Method: Systematic review and meta-analysis. Multiple database searches identified randomised placebo controlled trials of herbal interventions reporting at least one primary outcome measure. Where possible data were combined for meta-analysis. Primary outcome measures were lung function, exacerbations and reduction in corticosteroid use. Secondary outcome measures were symptoms and symptom scores, use of reliever medications, changes in rates of consultation and adverse effects.
Results: Twenty-six studies reporting on 20 herbal preparations were included. Two of six studies reporting change in FEV1 were positive. Little data was available on frequency of exacerbations. For primary outcomes single studies of Boswellia, Mai-Men-Dong-Tang, Pycnogenol, Jia-Wei-Si-Jun-Zi-Tang and Tylophora indica showed potential to improve lung function, and a study of 1.8-Cineol (eucalyptol) showed reduced daily oral steroid dosage.
Conclusions: Improvements in symptoms were not strongly supported by objective changes. Most trials were of small sample size, short duration, and poor methodology. Further adequately powered trials are needed to assess these compounds. Such trials should conform to CONSORT guidance, report standardised spirometry, and use validated symptom and severity scores. No recommendations for herbal treatment of asthma can be made from the current evidence.