A critical scoping review of external uses of comfrey (Symphytum spp.)

External preparations of the herb comfrey (most commonly Symphytum officinale L.) are widely available for over-the-counter, practitioner and healthcare professional usage. Traditional practice suggests comfrey can be used to treat musculoskeletal disorders, wounds and various other conditions; however a full and critical coverage of the evidence base has not yet been undertaken.

A critical scoping review was undertaken. Six bibliographic databases, 10 grey literature databases and nine trials registers were searched plus reference lists of included studies and a descriptive overview of comfrey. Randomised or non-randomised clinical trials assessing the external use of comfrey for any indication were included and methodological and reporting quality were assessed. Observational studies were included only in the assessment of adverse events. Studies were grouped and summarised according to the type of indication treated.

Of 1348 identified records, 64 full texts were screened for inclusion and 26 were included in the review - 13 RCTs, 5 non-randomised controlled trials and 8 observational studies evaluating treatments for ankle distortion, back pain, abrasion wounds, venous leg ulcers and osteoarthritis. The majority of included trials had an overall unclear risk of bias due to poor quality of reporting. Few adverse events were reported.

Individual clinical trials showed evidence of benefit for ankle distortion, back pain, abrasion wounds and osteoarthritis. Topical application appears to be safe but further rigorous assessment is needed. Systematic reviews focussing on particular indications may clarify the treatment effect and safety of external comfrey preparations.