Objective: The aim of this review is to evaluate and summarize the available scientific information on the commonest plant extracts marketed in Western countries. In view of the intense, ongoing search for new plant extracts with powerful anti-inflammatory activity, we paid particular attention to this topic. The aim is to provide broad coverage of as many potentially useful plants as possible and then to focus on those with the greatest therapeutic potential.
Methods: Our bibliographic sources were the SciFinder databases: CAPLUS, MEDLINE, REGISTRY, CASREACT, CHEMLIST, CHEMCATS (update to October 2007). In order to assess the value of clinical trials, we focused a specific search on clinical investigations concerning nine plants with the most trial data, viz., Althaea officinalis, Calendula officinalis, Centella asiatica, Echinacea purpurea, Passiflora incarnata, Punica granatum, Vaccinium macrocarpon, Vaccinium myrtillus, Valeriana officinalis. This was carried out in several databases (update to June 2008): ISI Web of Knowledge(SM) (ISI WoK), SciFinder (CAPLUS, MEDLINE, REGISTRY, CASREACT, CHEMLIST, CHEMCATS) and PubMed (indexed for MEDLINE).
Results: Our survey covers roughly a 1000 plants, although clinical trials have been published only for 156 plants supporting specific pharmacological activities and therapeutic applications. However, for about half of the plants, in vitro and in vivo studies provide some support for therapeutic use. For one-fifth of the plants included in our search, only phytochemical studies were found. Their properties and indications were often attributed to the presence of certain compounds, but no evidence concerning the activities of the whole extracts was presented. We found that for about 12% of the plants, currently available on the Western market, no substantial studies on their properties had been published, while there was strong evidence that 1 in 200 were toxic or allergenic, so that their use ought to be discouraged or forbidden. Nine plants had considerable evidence of therapeutic effect, viz., A. officinalis, Calendula officinalis, Centella asiatica, E. purpurea, Passiflora incarnata, Punica granatum, Vaccinium macrocarpon, Vaccinium myrtillus, Valeriana officinalis.
Conclusion: The present review provides a baseline on the level of evidence available on many herbal preparations and should be of help to those intending to research further on these topics.