The objective of this systematic review was to assess the evidence from rigorous clinical trials, systematic reviews and meta-analyses on the effectiveness of dietary supplements in reducing body-weight. Literature searches were conducted on Medline, Embase, Amed, Cinahl and the Cochrane Library until March 2003. Hand searches of medical journals, the authors’ own files and bibliographies of identified articles were conducted. There were no restrictions regarding the language of publication. The screening of studies, selection, validation, data extraction and the assessment of methodological quality were performed independently by the two reviewers. To be included, trials were required to be randomised and double blind. Systematic reviews and meta-analyses of dietary supplements were included if they were based on the results of randomised, double-blind trials. Five systematic reviews and meta-analyses and 25 additional trials were included and reviewed. Data on the following dietary supplements were identified: chitosan, chromium picolinate, Ephedra sinica, Garcinia cambogia, glucomannan, guar gum, hydroxy-methylbutyrate, Plantago psyllium, pyruvate, yerba mate and Pausinystalia yohimbe. The reviewed studies provide some encouraging data but no evidence beyond a reasonable doubt that any specific dietary supplement is effective for reducing body-weight. The only exceptions are E. sinica- and ephedrine-containing supplements, which have been associated with an increased risk of adverse events.