A Review of Herbal Treatments for Viral Respiratory Tract Infections
Viral respiratory infections (VRIs) like the common cold, viral pharyngitis, acute bronchitis, and influenza (flu) are among the most common human illnesses. Annual vaccines for flu lack acceptance and have variable efficacy. There are no vaccines for other VRIs, and the flu vaccine cannot prevent them. Conventional treatments for VRIs are generally lacking; even neuraminidase inhibitors (e.g., oseltamivir, zanamivir) are only marginally effective, with substantial adverse effects (AEs). Antibiotics do not affect viruses; nonetheless, lacking effective conventional medicines, patient demand for antibiotics continues, contributing to bacterial resistance. Many herbal medicines are used to prevent and treat VRIs. Some are backed by research; others, by traditional use; some, by both. Generally, no one herb can resolve VRIs. Multi-herb treatments tailored to the patient are most effective. Yarnell discusses a range of herbs useful for treating and/or preventing VRIs, adding his insights as a clinician.
Many herbs act directly against the viruses that cause VRIs and have broad clinical efficacy. Those tested against a range of organisms and viruses have been found to act against most. Listed are garlic (Allium sativum, Amaryllidaceae), licorice (Glycyrrhiza spp., Fabaceae) bloody cranes-bill (Geranium sanguineum, Geraniaceae), Umckaloabo (Pelargonium sidoides, Geraniaceae), Japanese honeysuckle (Lonicera japonica, Caprifoliaceae), black elderberry (Sambucus nigra, Adoxaceae) fruit, and others from diverse plant families. Black elderberry fruit and flower have been shown in clinical trials to reduce the severity and duration of flu symptoms. A proprietary formula (BNO1016; Sinupret; Bionorica SE; Neumarkt, Germany) uses a combination of black elderberry flower, vervain (Verbena officinalis, Verbenaceae), cowslip (Primula veris, Primulaceae), Rumex spp. (Polygonaceae), and yellow gentian (Gentiana lutea, Gentianaceae). The formula is active against parainfluenza, respiratory syncytial virus (RSV), rhinovirus, and adenovirus in vitro and has been shown to modulate inflammation in rodents. Randomized, placebo-controlled clinical trials (RCTs) in patients with VRIs also document BNO1016’s efficacy. RCTs included children and adults, with minimal AEs. The formula is also effective for allergies, sometimes clinically indistinguishable from VRIs. Among other anti-viral species, both Andrographis (Andrographis paniculata, Acanthaceae) and Umckaloabo have been found more effective than placebo, as well as safe, in meta-analyses of RCTs.
Yarnell also discusses two ephedra-based anti-viral remedies. Má huáng tāng, a traditional Chinese medicine (TCM) formula with ephedra (Ephedra sinica, Ephedraceae) and three other herbs, was first described for use in “cold damage diseases” in 220 CE. Its historical use against flu has been validated in modern studies. A variant, antiwei formula, adds three more herbs to the mix. In a Chinese RCT of 480 adults with flu (n=125) or flu-like illness (n=355), symptom duration and severity were significantly less in those who took antiwei formula compared to placebo. In these trials of ephedra medicines, AEs were uncommon and mild.
Plant families and species with known inflammation- and immuno-modulating effects, as well as anti-viral activity, include an Apiaceae group (oshá [Ligusticum spp.], lomatium [Lomatium dissectum], and western sweet cicely [Osmorhiza occidentalis]). Oshá and related species are used worldwide for colds and flu. Ligusticum spp. produce a known anti-viral compound, (Z)-ligustilide. A Lamiaceae group includes sage (Salvia officinalis), white sage (S. apiana), thyme (Thymusspp.)*, rosemary (Rosmarinus officinalis), and heal-all (Prunella vulgaris). An “evergreen” group spans three Pinaceae (pine [Pinus spp.], fir [Abies spp.], and spruce [Picea spp.]) and two Cupressaceae (cedar [Thuja spp.] and juniper (Juniperus spp.]) genera. Their resin and branch tips are antiviral and inflammation modulating, with an affinity for the respiratory tract. Evergreens are highly sustainable herbal sources. Since herbs in these three groups are immunomodulatory, their ability to also regulate inflammation reduces risks of worsening symptoms through a “cytokine storm.” Lomatium lowers production of CXCL10, highly associated with cytokine storms in severe flu. Other herbs reduce production of CCL5, another cytokine storm participant. Diterpenoids in rosemary and sage inhibit many such cytokines.
Echinacea (Echinacea Angustifolia, Asteraceae), a North American traditional VRI remedy, is an example of how poorly-informed research can harm the reputation of a useful herb. Studies have used extracts, dosages, durations, and means of administration with little or no traditional basis. When low doses at short duration proved ineffective, succeeding trials used even lower doses, citing poor results as proof of echinacea’s uselessness. Many used other Echinacea spp., alone or with E. angustifolia. While all Echinacea spp. show inflammation-modulating effects in VRI models in vitro, E. angustifolia is considered superior. Echinacea products must be gargled for their topical numbing effect, useful in pharyngeal pain.
Yarnell’s base formula for acute VRIs includes E. angustifolia, lomatium, heal-all, licorice, and pokeweed (Phytolacca americana, Phytolaccaceae), the latter a lymphagogue. For patients with confirmed flu, elderberry fruit should be added; for those with fever >103°F, febrifuge herbs. Other herbs can help patients without fever, those with bothersome coughs (wet and dry), or a sore throat.
Botanical extracts with significant potential to prevent VRIs include Asian ginseng (Panax ginseng, Araliaceae), American ginseng (P. quinquefolius), green tea (Camellia sinensis, Theaceae), and garlic. Given that many safe herbs can prevent and treat VRIs, the author urges “large-scale adoption” of these remedies.
* In an RCT in patients with acute bronchitis, a combination of thyme and ivy (Hedera helix, Araliaceae) leaf reduced coughing significantly more than placebo.
Yarnell E. Herbs for viral respiratory infections. Altern Complement Ther. February 2018;24(1):35-43. https://doi.org/10.1089/act.2017.29150.eya.