Antiviral agents from plants and herbs: a systematic review

Many antiviral compounds presently in clinical use have a narrow spectrum of activity, limited therapeutic usefulness and variable toxicity. There is also an emerging problem of resistant viral strains. This study was undertaken to examine the published literature on herbs and plants with antiviral activity, their laboratory evaluation in vitro and in vivo, and evidence of human clinical efficacy.

Independent literature searches were performed on MEDLINE, EMBASE, CISCOM, AMED and Cochrane Library for information on plants and herbs with antiviral activity. There was no restriction on the language of publication. Data from clinical trials of single herb preparations used to treat uncomplicated viral infections were extracted in a standardized, predefined manner.

Many hundreds of herbal preparations with antiviral activity were identified and the results of one search presented as an example. Yet extracts from only 11 species met the inclusion criteria of this review and have been tested in clinical trials. They have been used in a total of 33 randomized, and a further eight nonrandomized, clinical trials. Fourteen of these trials described the use of Phyllanthus spp. for treatment of hepatitis B, seven reporting positive and seven reporting negative results. The other 10 herbal medicines had each been tested in between one and nine clinical trials. Only four of these 26 trials reported no benefit from the herbal product.

Though most of the clinical trials located reported some benefits from use of antiviral herbal medicines, negative trials may not be published at all. There remains a need for larger, stringently designed, randomized clinical trials to provide conclusive evidence of their efficacy.