Review
Copyright ©The Author(s) 2021.
World J Gastroenterol. Oct 21, 2021; 27(39): 6551-6571
Published online Oct 21, 2021. doi: 10.3748/wjg.v27.i39.6551
Table 1 Antiviral effects of plants on respiratory viruses
Plant name
Preparation
Susceptible viruses
Ref.
Allium sativum (Garlic)Aqueous extracts Influenza A (H9N2)Rasool et al[53], 2017
ExtractInfectious bronchitis virus Mohajer Shojai et al[54], 2016
Ethanolic extractInfluenza A (H1N1)Chavan et al[55], 2016
Garlic oilInfluenza A (H1N1)Choi[56], 2018
Fresh extractInfluenza A (H1N1)Mehrbod et al[57], 2013
Aqueous extractAdenovirus (ADV3 and ADV41)Chen et al[58], 2011
Aloe vera (Aloe)Aloe anthraquinones and several derivatives (3-O-tetraacetoglupiranosil)Influenza A Borges-Argáez et al[59], 2019
Aloe-emodinInfluenza A Li et al[60], 2014
Astragalus mongholicus (Astragalus)Astragalus polysaccharidesAvian infectious bronchitis virus Zhang et al[61], 2018
Astragalus polysaccharideInfluenza A (H9N2)Kallon et al[62], 2013
Camellia sinensis (Green tea)Catechins -EGCGAdenovirusWeber et al[63], 2003
CatechinInfluenza AKuzuhara et al[64], 2009
CatechinsInfluenza A (H5N1)Liu et al[65], 2012
PolyphenolsInfluenza A; Influenza B Yang et al[66], 2014
Curcuma longa (Turmeric)CurcuminInfluenza A virus Chen et al[67], 2013
Dai et al[68], 2018
Curcumin Influenza A (H1N1, H6N1)Chen et al[69], 2010
CurcuminRSVObata et al[70], 2013
Echinacea purpurea (Purple coneflower)E. purpurea fresh herb and root tincturesInfluenza Vimalanathan et al[71], 2013
Standardized E. purpurea extractInfluenza A (H5N1, H7N7, H1N1) Pleschka et al[72], 2009
Standardized E. purpurea extractRhinoviruses, RSVHudson et al[73], 2011
Eucalyptus globulus (Eucalyptus)Essential oil- vapor phaseInfluenzaVimalanathan et al[74], 2014
Ginkgo biloba (Ginkgo)Leaf extractInfluenza A (H1N1, H3N2)Haruyama et al[75], 2013
Glycyrrhiza sp. (Licorice)Water extract of licorice (Glycyrrhiza uralensis)RSVFeng Yeh et al[76], 2013
Glycyrrhizic acid derivativesSARS-CoVHoever et al[77], 2005
Extract of Glycyrrhiza inflataInfluenza A (H1N1)Dao et al[78], 2011
GlycyrrhizinInfluenza AWolkerstorfer et al[79], 2009
GlycyrrhizinInfluenza A (H5N1)Michaelis et al[80], 2010
Lepidium meyenii (Maca)Extracted with methanolInfluenza A; Influenza B Del Valle Mendoza et al[81], 2014
Melaleuca alternifolia (Tea tree)Tea tree oilInfluenza A (H1N1)Garozzo et al[82], 2011
Aerosol and vapor of tea tree oilInfluenza A (H11N9)Usachev et al[83], 2013
Tea tree oilInfluenza A (H11N9)Pyankov et al[84], 2012
Melissa officinalis (Lemon balm)Essential oilInfluenza A (H9N2)Pourghanbari et al[85], 2016
ExtractAvian infectious bronchitis Lelešius et al[86], 2019
Mentha piperita (Peppermint)Ethanol extractRSVLi et al[87], 2017
ExtractAvian infectious bronchitis Lelešius et al[86], 2019
Nigella sativa (Black cumin)Ethanol extracts ofInfluenza A (H5N1)Dorra et al[88], 2019
Ethanol extracts ofInfluenza A (H9N2)Umar et al[89], 2016
ExtractCoronavirusUlasli et al[90], 2014
Panax ginseng (Ginseng)Root of plant Panax ginsengRSVLee et al[91], 2014
Panax Korean red ginseng extractRSVLee et al[92], 2014
Red ginseng extract and polysaccharide and saponin fractionsInfluenza A (H1N1)Yin et al[93], 2013
Korean red ginseng extractInfluenza A (H1N1, H3N2)Yoo et al[94], 2012
Pelargonium sidoides (Pelargonium)Pelargonium sidoides radix extract EPs® 7630RhinovirusRoth et al[95], 2019
EPs® 7630Respiratory virusesMichaelis et al[96], 2011
EPs® 7630Influenza A (H1N1, H3N2)Theisen et al[97], 2012
Sambucus nigra (Black elder)ExtractInfectious bronchitis virus Chen et al[98], 2014
Standardized elderberry liquid extractInfluenza A; Influenza BKrawitz et al[99], 2011
Concentrated juice of elderberryInfluenza AKinoshita et al[100], 2012
Elderberry flavonoidsInfluenza A (H1N1)Roschek et al[101], 2009
Scutellaria baicalensis (Chinese skullcap)Chemical constituentsInfluenza A (H1N1)Ji et al[102], 2015
BaicalinSARS-CoVChen et al[103], 2004
Torreya nucifera (Japanese nutmeg yew)Ethanol extract SARS-CoVRyu et al[104], 2010
Thymus vulgaris (Thyme)Essential oil- liquid phaseInfluenza Vimalanathan et al[74], 2014
ExtractAvian infectious bronchitis Lelešius et al[86], 2019
Withania somnifera (Ashwagandha)Withaferin AInfluenza A (H1N1)Cai et al[105], 2015
Zingiber officinalis (Ginger)Aqueous extracts Influenza A (H9N2)Rasool et al[53], 2017
Ethanol extractsInfluenza A- (H5N1)Dorra et al[88], 2019
Fresh gingerRSVChang et al[106], 2013
Table 2 Human clinical studies showing the effect of plants on respiratory infections
Plant
Disease state
Participant
Dosage
Study design
Results
Aged garlic extract[107]Cold andflu illness120 healthy subjects, 2 groups (21-50 yr)4 capsules/d (2.56 g); 90 dDouble-blind, randomized, placebo-controlled parallel interventionIncrease in γδ-T cell and NK cell. Reduction in cold and flu severity; decrease in symptom days
E. purpurea and E. angustifolia root[108]New-onset common cold719 patients, 4 parallel groups (12-80 yr)First 24 h: Equivalent of 10.2 g of root. Next 4 d: 5.1 gRandomized, controlled trialDisease duration and severity are not statistically significantly changed
Echinacea purpurea alcohol extract (Echinaforce®)[109]Common cold755 healthy subjects, 2 groups (≥ 18 yr)Illness prevention: 3 × 0.9 mL. Acute stages of colds: 5 × 0.9 mLRandomized, double-blind, placebo-controlled trialReduction of the total number of cold episodes, cumulated episode days, and pain-killer medicated episodes. Inhibited virally confirmed colds and especially prevented enveloped virus infections. Maximal effects on recurrent infections. Prophylactic intake of E. purpurea over a period of 4 mo to provide a positive risk/benefit ratio
Echinacea root extract[110]Respiratory symptoms175 adults, 2 groups (18–65 yr)Tablets: 112.5 mg E. purpurea 6:1 extract (equivalent to 675 mg dry root) and 150 mg E. angustifolia 4:1 extract (equivalent to 600 mg dry root) 3 × 1 tablet, if required: 3 × 2 tabletsRandomized, double blind, placebo-controlled trialLower respiratory symptom scores. Preventive effect against the development of respiratory symptoms during travel, including long-haul flights
Green tea catechins and theanine[111]Influenza200 healthcare workers, 2 groupsCapsules: Green tea catechins (378 mg/d) and theanine (210 mg/d). 5 mRandomized, double-blind, placebo-controlled trialLower incidence of influenza infection in the catechin/theanine group
Ivy leaf extract[112]Acute or chronic bronchial inflammatory disease9657 patients (5181 children)Ivy leaves extract [drug-to-extract ratio: 5-7.5:1; extraction solvent: ethanol 30% (w/w)]. 0–5 yr: 3 × 2.5 mL; 6–12 yr: 3 × 5 mL; 12 yr and adults: 3 × 5–7.5 mL. 7 dProspective, open, multicenter post marketing studyHealing or improvement in 95% of symptoms. Effective and well tolerated
Ivy extract (Hedelix®)[113]Acute respiratory catarrh and/or chronic recidivating inflammatory bronchial disease268 children, 2 groups (syrup and drops groups) (0-12 yr)0-1 yr: 1 × 2.5 mL syrup or 3 × 5 drops, 1-4 yr: 3 × 2.5 mL syrup or 3 × 16 drops, 4-10 yr: 4 × 2.5 mL syrup or 3 × 21 drops, 10-12 yr: 3 × 5 mL syrup or 3 × 31 drops. 14 dIndependent open, non-interventional studiesEffective and safe treatment of cough. Reduction in symptoms (especially rhinitis, cough and viscous mucus)
Ivy leaves dry extract (Prospan ®)[114]Bronchial asthma30 children (suffering from partial or uncontrolled mild persistent allergic asthma despite long-term treatment with 400 μg budesonide equivalent), 2 groups (6–11 yr)2 × 5 mL (corresponding to 70 mg extract) 28–30 dRandomized, double blind, placebo-controlled, cross-over studyImprovement of MEF75-25, MEF25 and VC
Korean red ginseng extract[115]Influenza-like illness100 healthy adults, 2 groups (30-70 yr)9 capsules/d. 3 mPlacebo-controlled trialReduced the incidence of influenza-like illness
Modified ginseng extracts (GS-3K8 and GINST)[116]Acute respiratory illness45 healthy applicants, 3 groups (39-65 yr)Capsules: 500 mg; 6 capsules/d; 8 wkRandomized, double-blind, placebo-controlled pilot studyReduction in acute respiratory illness development and symptom duration
Panax quinquefolius extract CVT-E002[117]Acute respiratory illness and Chronic Lymphocytic Leukemia293 patients, 2 groups (≥ 18 yr)2 × 200 mg extract. 3 mRandomized, double-blind, placebo-controlled studyReduction intense acute respiratory illness and moderately-severe sore throat. Increased antibody responses.
Panax ginseng[118]Chronic obstructive pulmonary disease14 participants, 2 groups (57–73 yr)2 × 200 mg 4 wkClinical trial protocol and pilot studyOne participant in P. ginseng group reported events of sore throat, cough and fever
Panax ginseng root extract[119]Chronic obstructive pulmonary disease168 participants, 2 groups2 × 100 mg capsules. 24 wkRandomized, multi-center, double-blind, placebo controlledReduction in symptoms
Pelargonium sidoides extract EPs® 7630[120]Chronic obstructive pulmonary disease199 adults, 2 groups (18 yr and older)30 drops. 24 wkRandomized, double-blind, placebo-controlled, parallel group trialImprovement in HRQoL (health-related quality-of-life) and PRO (Patient-reported outcomes)
Pelargonium sidoides extract EPs® 7630[121]Acute bronchitis220 patients (1-18 yr)1-6 yr: 3 × 10 drops; 6–12 yr: 3 × 20 drops; 12-18 yr: 3 × 30 drops; 7 dRandomized, double-blind, placebo-controlled clinical trialReduction in the total score of bronchitis-specific symptoms (especially cough and rales at auscultation)
Pelargonium sidoides extract EPs® 7630[122]Upper respiratory tract infections28 children with a diagnosed transient hypogammaglobulinemia of infancy (1-5 yr)3 × 10 drops; 7 dRandomized, placebo controlled, prospective, monocentric pilot studyIncreased appetite. Reduction of nasal congestion
Pelargonium sidoides root extract EPs® 7630[123]Upper respiratory tract- asthma attacks61 children (1–14 yr)1–5 yr: 3 × 10 drops; 6–12 yr: 3 × 20 drops; 12 yr and above: 3 × 30 drops; 5 dRandomized, placebo controlledReduction the severity of symptoms (especially cough and nasal congestion). Shortening of the duration of upper respiratory viral infections. Reduction asthma attack frequency
Pelargonium sidoides preparation EPs® 7630[124]Acute non-streptococcal tonsillopharyngitis126 children, 2 groups (6–10 yr)3 × 20 drops. 6 dDouble-blind, placebo-controlled clinical trialDecrease in tonsillitis severity score compared to placebo in the EPs® 7630 group after 4 d of treatment
Pelargonium sidoides extract EPs® 7630[125]Common cold207 adults (18-55 yr)SD: 3 × 30 drops; HD: 3 × 60 drops; 10 dProspective, double-blind, parallel-group, placebo-controlled, phase 3, 2 parts, 2-arm, clinical trialAfter 10 d, clinical treatment in 90.4% of the active drug group. Reduction the severity of symptoms and short the duration of the disease. Higher full recovery rates or greater recovery for HD treatment on day 5
Sambucus nigra extract[126]Influenza64 patients (16-60 yr)Lozenge: 175 mg extract; 4 lozenges/d; 2 dRandomized, double-blind, placebo-controlled, pilot clinical trialsSignificant improvement in most symptoms within 24 h (fever, headache, muscle aches and nasal congestion). Significant improvement in all investigated symptoms within 48 h (cough and mucus discharge)
Sambucus nigra extract[127]Respiratory health312 adults, 2 groupsCapsules: 300 mg. Before travel: 2 capsules/d. During travel and after arrival: 3 capsules/d. 14 dRandomized, double-blind placebo-controlled clinical trialReduction of cold duration and severity in air travelers. Low symptom score
Table 3 Plants that can have an impact on coronavirus disease 2019 symptoms
Plant name
Effects
Ref.
Allium sativum (Garlic)AnalgesicDehghani et al[128], 2018
Anti-inflammatoryArreola et al[129], 2015
Anti-plateletHiyasat et al[130], 2009
Heart protectionSultana et al[131], 2016
Hepatic protectionAprioku et al[132], 2017
Improving GI functionChen et al[133], 2018
Renal protectionSeckiner et al[134], 2014
Curcuma longa (Turmeric)AnalgesicHenrotin et al[135], 2020
Eke-Okoro et al[136], 2018
Antiemetic Liu et al[137], 2018
AntifatigueHuang et al[138], 2015
Anti-inflammatoryShimizu et al[139], 2019
AntifibroticGouda et al[140], 2019
AntipyreticHaider et al[141], 2013
BronchodilatorRam et al[142], 2003
GI protectionHaider et al[141], 2013
Dulbecco and Savarino[143], 2013
Hepatic protectionDulbecco and Savarino[143], 2013
Glycyrrhiza glabra (Licorice)AntitussivesNosalova et al[144], 2013
Kuang et al[145], 2018
Anti-inflammatoryKao et al[146], 2010
Respiratory system protectionShi et al[147], 2011
Nigella sativa (Black cumin)AnalgesicRushmi et al[148], 2017
AnticoagulantMuralidharan-Chari et al[149], 2016
AntihistaminicAnsari et al[150], 2010
Alsamarai et al[151], 2014
Anti-inflammatoryMajdalawieh and Fayyad[152], 2015
Mahdavi et al[153], 2016
BronchodilationBoskabady et al[154], 2010
Salem et al[155], 2017
Panax ginseng (Ginseng)AdaptogenicRatan et al[156], 2021
Pelargonium sidoides (Pelargonium)AntitussivesBao et al[157], 2015
Secretolytic activityBao et al[157], 2015
Scutellaria baicalensis (Chinese skullcap)AntiemeticAung et al[158], 2005
Anti-inflammatoryHong et al[159], 2013
GI protectionMehendale et al[160], 2007
Cui et al[161], 2021
Hepatic protectionThanh et al[162], 2015
NeuroprotectiveDai et al[163], 2013
Regulation of histamine release-Anti allergicBui et al[164], 2017
Thymus vulgaris (Thyme)AnalgesicLaub[165], 2018
Salmalian et al[166], 2014
Anticoagulant Okazaki et al[167], 2002
Anti-inflammatoryHabashy et al[168], 2018
Withania somnifera (Ashwagandha)AdaptogenicSalve et al[169], 2019
AnalgesicMurthy et al[170], 2019
Anticoagulant, antithromboticKu et al[171], 2014
Anti-inflammatory Gupta and Singh[172], 2014
AntitussivesNosalova et al[144], 2013
Stress-relievingLopresti et al[173], 2019
Zingiber officinale (Ginger)AnalgesicMaghbooli et al[174], 2014
Bartels et al[175], 2015
AntiemeticTóth et al[176], 2018
Anti-inflammatoryKhan et al[177], 2015
Antiplatelet, antithromboticLee et al[178], 2017
AntitussivesBera et al[179], 2016
GI protectionNanjundaiah et al[180], 2011
Hepatic protectionAjith et al[181], 2007
NephroprotectiveAjith et al[182], 2007
Table 4 Angiotensin-converting enzyme inhibitor plant
Plants
The compound under study
Results
Ref.
Ammoides verticillata essential oilIsothymolSARS-CoV-2/ACE2 inhibitionAbdelli et al[183], 2021
Allium sativum essential oilOrganosulfur compounds (99.4% of its essential oil)SARS-CoV-2/ACE2 inhibition. Garlic essential oil can prevent protein maturation of the virus and the spread of infectionThuy et al[184], 2020
Apium graveolensApigeninKidneys of spontaneous hypertensive rats/Regulation in ACE2 expressionSui et al[185], 2010
Camellia sinensisBlack tea; Dark tea; Green tea; Oolong tea; White teaACE inhibition: Green < oolong < white < black < dark teasDong et al[186], 2011
Citrus aurantiumHesperetin. Scutellarin. Nicotianamine. Glycyrrhizin. BaicalinSARS-CoV-2/Connecting to ACE2 and blocking the SARS-CoV-2 inputChen and Du[187], 2020
Erigeron breviscapus
Glycine max
Glycyrrhiza radix
Scutellaria baicalensis
Geranium and lemon essential oilsCitronellol and limoneneSARS-CoV-2/ACE2 inhibitionSenthil Kumar et al[188], 2020
Ginseng Glycyrrhiza uralensisGinsenoside Rg6; Ginsenoside F1; Monoammonium glycyrrhizinate; Glycyrrhizic acid methyl esterSARS-CoV-2/ACE2 kinase inhibitionZi et al[189], 2020
Glycine max (soybean)NicotianamineACE2 inhibitionTakahashi et al[190], 2015
Glycyrrhiza glabraGlycyrrhizic acidSARS-CoV-2/Glycyrrhizic acid disrupts the connection of the virus with the ACE2 receptor at the entry levelSinha et al[43], 2021
Hibiscus sabdariffa anthocyaninsDelphinidin- and cyanidin-3-O-sambubiosidesACE inhibitionOjeda et al[191], 2010
Linum usitatissimum (Flaxseed)Secoisolariciresinol diglucosideACE inhibitionPrasad et al[192], 2013
Melaleuca cajuputi essential oilComponents (70.9% of the oil)SARS-CoV-2/ACE2 and PDB6LU7 proteins inhibitionMy et al[193], 2020
Nicotiana benthamianaRecombinant ACE2-Fc fusion protein produced from N. benthamianaSARS-CoV-2/Strong binding to the RBD of SARS-CoV-2 and inhibitionSiriwattananon et al[194], 2020
Withania somniferaWithanoneSARS-CoV-2/Docking to the connector interface of the AEC2-RBD complexBalkrishna et al[51], 2020