To evaluate the efficacy of Western herbal medicines in the treatment of irritable bowel syndrome (IBS).A computer-based search of MEDLINE, EMBASE, CINAHL, AMED, GreenFILE, Health Source: Nursing/Academic Edition, and the Cochrane Library was conducted. A hand-search of the bibliographies of relevant papers and previous meta-analyses and reviews was also undertaken. Trials were included in the review if they were double-blind and placebo-controlled investigating the effects of Western herbal medicines on IBS-related symptoms or quality of life. There were no language restrictions. Eligibility assessment and data extraction were performed by two independent researchers. For herbal medicines where there was more than 1 trial of similar design, data were synthesised using relative risk of symptoms improving using the random effects model.Thirty-three trials were identified that met all eligibility criteria. Seventeen of these evaluated peppermint essential oil, fifteen other Western herbal medicines, and one trial evaluated peppermint oil in one arm and aniseed essential oil in the other arm. Eighteen different herbal preparations were evaluated in these trials. Data suggests that a number of Western herbal medicines may provide relief of IBS symptoms. Meta-analyses suggest that peppermint essential oil is both efficacious and well-tolerated in the short-term management of IBS. Aloe vera and asafoetida also demonstrated efficacy in reducing global IBS symptoms in meta-analyses. The herbal formulas STW 5, STW 5-II and Carmint, along with Ferula assa-foetida, Pimpenella anisum oil, the combination of Curcumin and Foeniculum vulgare oil, and the blend of Schinopsis lorentzii, Aesculus hippocastanum, and peppermint essential oil also demonstrated efficacy in rigorously-designed clinical trials.A number of Western herbal medicines show promise in the treatment of IBS. With the exception of peppermint essential oil, Aloe vera, and asafoetida, however, none of the positive trials have been replicated. This lack of replication limits the capacity to make definitive statements of efficacy for these herbal medicines.