Many hundreds of plants worldwide have a place in folk medicine as treatments for microbial infections and antimicrobial activity of extracts in vitro may be readily assessed in microbiology laboratories. Many so tested are reported to show inhibitory effects against a range of organisms. For less than responsible entrepreneurs, this is often enough reason to promote them as therapeutic options.
But laboratory testing can at best be only a very crude, though relatively inexpensive and rapid screen, while in vivo testing is very costly and time consuming. On this background, we conducted a review in 2003 to examine the range of plants or herbs that have been tested for antiviral properties in laboratories, animals and humans. Here is its abstract:
Background and aims: 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.
Methods: 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.
Results: 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 randomised, and a further eight non-randomised, 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.
Conclusions: 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most of the clinical trials located reported some benefits from use of antiviral herbal medicines, negative trials may not be published at all.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, randomised clinical trials to provide conclusive evidence of their efficacy.
One of the herbal remedies that seemed to show some promise specifically for upper respiratory infections was Andrographis paniculata. This evidence prompted us in 2004 to conduct a systematic review focused on this herb specifically. Here is its abstract:
Acute respiratory infections represent a significant cause of over-prescription of antibiotics and are one of the major reasons for absence from work. The leaves of Andrographis paniculata (Burm. f.) Wall ex Nees (Acanthaceae) are used as a medicinal herb in the treatment of infectious diseases. Systematic literature searches were conducted in six computerised databases and the reference lists of all papers located were checked for further relevant publications. Information was also requested from manufacturers, the spontaneous reporting schemes of the World Health Organisation and national drug safety bodies. No language restrictions were imposed. Seven double-blind, controlled trials (n = 896) met the inclusion criteria for evaluation of efficacy. All trials scored at least three, out of a maximum of five, for methodological quality on the Jadad scale. Collectively, the data suggest that A. paniculata is superior to placebo in alleviating the subjective symptoms of uncomplicated upper respiratory tract infection. There is also preliminary evidence of a preventative effect. Adverse events reported following administration of A. paniculata were generally mild and infrequent. There were few spontaneous reports of adverse events. A. paniculata may be a safe and efficacious treatment for the relief of symptoms of uncomplicated upper respiratory tract infection; more research is warranted.
Before you now rush to buy a dietary supplement of A. paniculata, let me stress this in no uncertain terms: the collective evidence is at best suggestive, but it is not compelling. Importantly, there is, to the best of my knowledge, no sound evidence that any herbal remedy is effective in preventing or treating Covid-19 infections.
I truly wished to be able to report more encouraging news, but the truth is the truth, even (I would argue, particularly) in desperate times.