1. Introduction: The Dual Burden of Respiratory Infections and Antimicrobial Resistance

Respiratory tract infections (RTIs) represent one of the most significant global health burdens, spanning a spectrum from mild upper respiratory conditions such as the common cold and pharyngitis to severe lower respiratory tract infections like pneumonia and bronchitis. These infections account for a substantial portion of outpatient visits and hospital admissions globally, with the burden disproportionately felt in low- and middle-income countries like Nigeria, where healthcare systems are already strained.

The challenge is compounded by a crisis of antimicrobial resistance (AMR). In Nigeria, the incidence of resistant pathogens has increased by 30% over the past decade. Antibiotic overprescription for viral RTIs—where antibiotics are ineffective—has accelerated this crisis. The World Health Organization estimates that over 1 million deaths annually are attributable to bacterial AMR, a figure projected to rise to 10 million by 2050. This has driven an urgent need to explore alternative and complementary therapeutic options that are accessible, affordable, and effective—a space where traditional herbal medicine in Nigeria holds significant promise.

Across Nigeria, approximately 90% of people in rural areas rely on herbs for their healthcare needs. For RTIs, this reliance is particularly pronounced: coughs, colds, sore throats, and chest complaints are among the most common ailments for which Nigerians seek herbal interventions. This review synthesises available literature on Nigerian medicinal plants utilised for RTI management, their modes of administration, scientific evidence supporting their use, and the broader context of holistic and complementary approaches.

2. Nigerian Herbal Remedies: Traditional Use and Scientific Evidence

2.1 Ethnobotanical Surveys: Documenting Respiratory Remedies

Ethnobotanical surveys across Nigeria have documented the diversity of plants used for respiratory conditions. A survey in Ogbomosho, Oyo State, focusing on COVID-19, cough, and flu, identified 31 medicinal plants for cough and 29 for flu. The most cited plant for COVID-19 and flu was Zingiber officinale (ginger), while Citrus limon (lemon) was the most cited for cough. Leaves were the most used plant part, with decoction and infusion as the primary preparation methods.

A comprehensive ethnobotanical survey in Damaturu, Yobe State, documented 20 plant species belonging to 14 families, with Fabaceae as the most represented family (25%). Respiratory infections such as colds were alleviated using Piliostigma reticulatum. Fever, often a symptom of respiratory infections, was treated with Boswellia papyrifera, Guiera senegalensis, and Azadirachta indica (neem).

An earlier ethnographic study across four local government areas revealed that for cough remedies, 39% of groups mentioned herbal drinks, 19.5% used honey with lemon, and 21.7% used preparations containing palm oil. This foundational research highlighted the deep-rooted reliance on home remedies for RTI management.

2.2 Plants with Documented Use for Respiratory Conditions

Based on the literature, the following plants are consistently documented for RTI management across Nigeria:

Plant Name	Common Name	Part Used	Documented Condition
Zingiber officinale	Ginger	Rhizome	COVID-19, flu, cough
Citrus limon	Lemon	Fruit	Cough, sore throat
Allium sativum	Garlic	Bulb	Respiratory infections, pneumonia
Azadirachta indica	Neem	Leaves, bark	Fever (associated with RTIs)
Garcinia kola	Bitter kola	Seed	Respiratory symptoms
Anogeissus leiocarpus	African birch	Roots, stem bark	Asthma, cough, tuberculosis
Moringa oleifera	Moringa	Root	Respiratory ailments
Nigella sativa	Black seed	Seed	Respiratory infections
Dennettia tripetala	Pepper fruit	Leaves, fruit	Cough, nasal congestion, fever
Piliostigma reticulatum	–	Various	Colds
Gongronema latifolium	Utazi (Igbo)	Leaves	Respiratory infections, pneumonia

2.3 Garcinia kola (Bitter Kola): A Staple for Respiratory Health

Garcinia kola Heckel, commonly known as bitter kola, is a woody plant native to West Africa that holds a prominent position in Nigerian traditional medicine. A questionnaire-based study involving 152 respondents, primarily from the Ibibio, Annang, and Igbo ethnic groups, documented that most participants reported using fresh seeds of bitter kola, mainly for treating respiratory symptoms .

The study concluded that several traditional uses of bitter kola are supported by scientific evidence, including its antioxidant and immunomodulatory effects, along with benefits for respiratory, gastric, and reproductive conditions. However, the authors emphasised that further studies are required to establish standardised dosages and safety profiles.

3. Scientifically Validated Herbal Formulations and Mechanisms

3.1 Antibacterial Activity of a Traditional Pneumonia Concoction

A study in Ondo State evaluated a traditional concoction prepared from Piper guineense (seeds), Zingiber officinale (rhizome), and honey—a formulation used in folk medicine to treat respiratory diseases.

Key Findings :

Parameter	Result
Zone of Inhibition (concoction)	31.25 to 37.75 mm
Zone of Inhibition (conventional antibiotics)	1.25 to 16.00 mm
Phytochemicals detected	Saponins, tannins, flavonoids, alkaloids, terpenoids, cardiac glycosides

The study demonstrated that the growth inhibition mediated by the traditional concoction was superior to that of the antibiotics used against the test pneumonic bacteria. The authors concluded that this formulation “could be exploited as alternative for treating bacterial pneumonia”. The potency of the combination—superior to antibiotics—likely arises from the synergistic activity of multiple phytochemicals.

3.2 Antimicrobial Peptides from Nigerian Plants

Research into host defence peptides (HDPs)—endogenous antibiotics produced by plants as part of their innate immune system—has revealed promising activity against respiratory pathogens. A study investigating peptide-rich extracts from seven Nigerian plant families (Rubiaceae, Apocynaceae, and Euphorbiaceae) found that the peptide-rich fractions of Nauclea diderrichii and Euphorbia hirta exhibited remarkable antimicrobial activity.

Key Findings :

Plant	MIC Against Bacteria	MIC Against Fungi
Nauclea diderrichii	7.8 µg/mL (gram-positive), 15.63-62.5 µg/mL (gram-negative)	7.8 µg/mL
Euphorbia hirta	Broad-spectrum activity	Demonstrated

These peptide fractions exhibited bactericidal activity (MIC index ≤4, >3 log10 reduction of initial inoculum) and validated the ethnomedicinal use of these plants in the management of diverse infectious diseases, including respiratory tract infections .

3.3 Antimycobacterial Activity Against Tuberculosis

Anogeissus leiocarpus, used traditionally in Nigeria for asthma, cough, and tuberculosis, demonstrated activity against Mycobacterium bovis (BCG) in an in vitro antimycobacterial evaluation. The hexane extract of the root bark showed a Minimum Inhibitory Concentration (MIC) of 312.5 µg/mL. This provides preliminary support for the traditional use of this plant in managing tuberculous respiratory infections.

4. The “Big Six” Herbal Remedies: Evidence Profiles

A meta-narrative review synthesised evidence from 18 studies on five natural remedies commonly used for RTI management: garlic, ginger, black seed, lemon, and honey. The review identified distinct evidence profiles for each remedy.

4.1 Honey: The Strongest Clinical Evidence

Key Findings:

Parameter	Result
Effect on cough symptoms	Superior to usual care, placebo, and diphenhydramine
Evidence base	Supported by Cochrane review and systematic reviews
Mechanism	Antimicrobial, soothing/demulcent, immunomodulatory

Honey demonstrated the strongest clinical evidence, with systematic reviews confirming its superiority for improving combined symptom scores, cough frequency, and cough severity. A Cochrane review concluded that honey is probably more effective than no treatment, diphenhydramine, and placebo for relieving cough symptoms in children. This evidence directly supports guidelines from bodies like the UK’s National Institute for Health and Care Excellence (NICE), which recommends honey for acute cough—a vital antimicrobial stewardship strategy in Nigeria’s context of rising AMR.

4.2 Nigella sativa (Black Seed): Promising Adjunctive Therapy

Key Findings:

Parameter	Result
Effect	Accelerated clinical recovery, supported immunomodulation
Mechanism	Anti-inflammatory, immunomodulatory, bronchodilatory
Safety	Safe for short-term use; mild digestive discomfort reported

Nigella sativa showed the ability to accelerate early clinical recovery when combined with standard treatments. Its anti-inflammatory and immunomodulatory properties, supported by a well-elucidated pharmacological profile, make it a multi-targeted therapeutic agent.

4.3 Zingiber officinale (Ginger): Bronchodilatory and Anti-Inflammatory

Key Findings:

Parameter	Result
Mechanism	Direct relaxation of airway smooth muscle via calcium channel modulation
Evidence type	Strong mechanistic evidence, limited clinical validation
Clinical trial	Ginger powder 1.5 g twice daily reduced COVID-19 quarantine duration by 2.4 days

Ginger’s potent bronchodilatory effect, mediated through calcium channel modulation in airway smooth muscle, provides a sophisticated scientific rationale for its traditional use in relieving cough and asthma. However, its limited impact on viral clearance in clinical trials highlights the distinction between mechanistic plausibility and patient-centred outcomes.

4.4 Allium sativum (Garlic): Potent In Vitro, Limited Clinical Validation

Key Findings:

Parameter	Result
In vitro activity	Potent antibacterial against multidrug-resistant pathogens
Clinical validation	Limited; mostly indirect evidence from polyherbal combinations
Mechanism	Broad-spectrum antimicrobial; allicin as active component

Garlic demonstrated consistent in vitro antibacterial activity against a wide range of multidrug-resistant respiratory pathogens, including Pseudomonas aeruginosa and Staphylococcus aureus. However, high-quality clinical trials on garlic alone for RTI symptoms in humans are notably absent.

4.5 Citrus limon (Lemon): Synergistic Partner

Key Findings:

Parameter	Result
Effectiveness	Most effective in synergistic combinations with honey and ginger
Mechanism	Antimicrobial, anti-inflammatory, rich in vitamin C
Evidence type	Primarily synergistic; limited efficacy as monotherapy

Lemon proved most effective in synergistic combinations (e.g., with honey and ginger) . Its antimicrobial effects were enhanced in combination, supporting traditional practices of using lemon with honey.

4.6 Gongronema latifolium (Utazi): Antitussive (Cough-Suppressing) and Antibacterial

Key Findings:  

Parameter	Result
Effectiveness	Most effective when the leaves are chewed
Mechanism	The antibacterial potency of the plant extract may be ascribed to the presence of antioxidative compounds like saponins, alkaloids, tannins, triterpenes, and cardiac glycosides in the plant leaves.
Evidence type	Scientific studies have provided compelling evidence for the traditional use of G. latifolium in treating respiratory infections.

A study concluded that the in vivo antibacterial potency of the plant extract may be ascribed to the presence of antioxidative compounds like saponins, alkaloids, tannins, triterpenes, and cardiac glycosides in the plant leaves.

5. Traditional Preparation and Administration Methods

5.1 Common Preparation Methods

Method	Description	Common Usage
Decoction	Boiling plant material in water	Most common for bark, roots, and tough leaves
Infusion	Steeping plant material in hot water (like tea)	Common for leaves and flowers
Steam inhalation	Inhaling steam from boiling herbal mixtures	Used during COVID-19; clears lungs
Concoction	Mixing multiple plant preparations with honey or alcohol	Common for polyherbal formulations
Chewing	Eaten the raw leaf	Common for G. latifolium

5.2 Specific Preparation Examples

COVID-19 and Respiratory Infection Remedies :

Recipe Description	Preparation	Duration
Lemon, ginger, turmeric, black pepper, garlic in hot water	Mixed in hot water, steam inhaled through nose for 20-30 min	Daily intake
Neem, lemongrass, ginger, mango leaves, guava leaves	Boiled together; steam inhaled	Every 4 days
Artemisia, neem leaves, pawpaw leaves, garlic, ginger, lime, oranges	Cooked together for 30 minutes; inhaled as it boils	7-14 days
Honey, garlic, ginger, lime	Blended to paste; scoop in hot water with tea	Every 4 hours

Dennettia tripetala (Pepper Fruit) :

• Leaf decoction for fever: Simmer 25 g of fresh leaves in 1 litre of water for 10-15 minutes; drink a cup 2-3 times daily for 1-2 days
• Chewing fruit for cough: Fresh fruits chewed to clear nasal congestion and relieve cough

6. Holistic and Complementary Therapies

6.1 Non-Plant Interventions

Beyond herbal remedies, traditional and complementary approaches include:

Intervention	Application	Evidence
Honey and lemon	Soothe sore throat, cough	Strong clinical evidence
Steam inhalation	Clear nasal congestion, loosen phlegm	Documented in COVID-19 management
Prayer and spiritual interventions	Complementary support	Documented practice
Palm oil preparations	Base for herbal applications	Documented in ethnographic study

6.2 Dietary and Lifestyle Support

• Hydration: Warm herbal teas help soothe the throat and maintain hydration
• Nutritional support: Vitamin C-rich fruits (lemon, pawpaw) support immune function
• Rest: Adequate rest allows the immune system to fight infection effectively
• Avoiding irritants: Smoke, dust, and cold water are perceived as causes of RTIs

7. Safety Considerations and Contraindications

7.1 Key Safety Concerns

Concern	Implication
Lack of standardisation	Variable potency and possible contamination
Drug interactions	Herbal remedies may interact with antibiotics, antihypertensives
Limited clinical trial data	Most evidence from in vitro and animal studies
Adverse effects	Mostly mild (gastrointestinal discomfort), but monitoring needed
Specific warnings	Dennettia tripetala may irritate sensitive mucosa; avoid in pregnancy

7.2 Safety Profile by Remedy

Remedy	Safety Profile	Adverse Events
Honey	Well-tolerated	Minor gastrointestinal upset
Garlic	Favourable safety profile	Mild digestive discomfort
Ginger	Favourable safety profile	Minimal adverse effects
Black seed	Safe for short-term use	Mild digestive discomfort
Utazi	Favourable safety profile	Mino digestive discomfort

7.3 Recommendations

For Patients and Families:

1. Consult healthcare practitioners for severe respiratory symptoms (shortness of breath, high fever, chest pain)
2. Disclose herbal medicine use to healthcare providers
3. Use products from reputable sources, preferably with NAFDAC registration
4. Do not rely solely on herbs for severe pneumonia or tuberculosis
5. Seek medical attention if symptoms worsen despite herbal treatment
6. Avoid self-treatment in pregnancy without professional guidance

For Healthcare Providers:

1. Ask about herbal medicine use during consultations
2. Provide evidence-based guidance on complementary therapies
3. Monitor for potential drug interactions with antibiotics
4. Support research on safety and efficacy of commonly used herbs
5. Document herbal use in patient records

For Researchers:

1. Conduct high-quality clinical trials on commonly used remedies (particularly garlic)
2. Evaluate safety profiles for chronic use
3. Study drug interactions with antibiotics and other medications
4. Identify and characterise active compounds

8. Research Gaps and Future Directions

8.1 Key Research Needs

Area	Priority
High-quality clinical trials	Most evidence from in vitro studies; human data needed
Ginger clinical trials	Only one RCT identified; more evidence needed
Garlic clinical validation	Potent in vitro but limited clinical proof
Standardised dosing protocols	Defined dosing for herbal formulations
Safety and toxicology profiles	Long-term safety data for commonly used herbs
Drug interaction studies	Interactions with antibiotics, antivirals
Mechanism of action studies	Cellular and molecular pathways

8.2 Opportunities

• Antimicrobial stewardship: Promoting honey as first-line treatment for uncomplicated cough could reduce inappropriate antibiotic prescriptions
• Synergy research: Investigating synergistic mechanisms in traditional formulations
• Host defence peptide research: Exploring plant-derived antimicrobial peptides for drug development
• Integration strategies: Combining herbal and conventional therapies

9. Conclusion

Respiratory tract infections represent a significant health burden in Nigeria, exacerbated by the dual challenges of limited healthcare access and rising antimicrobial resistance. Against this backdrop, Nigerian traditional medicine offers a rich repository of plant-based remedies, with scientific research increasingly validating their efficacy.

The literature reveals a diverse array of Nigerian plants with documented respiratory applications:

• Garcinia kola (bitter kola) is widely used for respiratory symptoms, with scientific support for antioxidant and immunomodulatory effects
• Concoctions of Piper guineense, Zingiber officinale, and honey demonstrated antibacterial activity superior to conventional antibiotics against pneumonic bacteria
• Peptide-rich fractions from Nauclea diderrichii and Euphorbia hirta showed potent broad-spectrum antimicrobial activity, validating ethnomedicinal use for RTIs

Meta-narrative synthesis identified distinct evidence profiles:

• Honey demonstrates the strongest clinical evidence, with superiority over usual care and conventional antitussives for cough relief
• Nigella sativa shows promise as adjunctive therapy with immunomodulatory effects
• Ginger has potent bronchodilatory properties with limited clinical validation
• Garlic demonstrates potent in vitro antimicrobial activity but limited clinical evidence
• Lemon is most effective in synergistic combinations

The path forward requires:

1. Acknowledging and respecting traditional knowledge while subjecting it to scientific scrutiny
2. Strengthening regulatory oversight of herbal products through NAFDAC
3. Promoting open communication between patients and healthcare providers
4. Investing in clinical research on safety, efficacy, and mechanisms of action
5. Developing integration strategies that combine the best of both systems
6. Supporting antimicrobial stewardship through evidence-based use of remedies like honey
7. Preserving and documenting indigenous knowledge before it is lost

As Nigeria continues to face the burden of respiratory infections and antimicrobial resistance, the careful integration of evidence-based traditional medicine into the healthcare system offers promising strategies for improving access to care and reducing reliance on ineffective or inappropriate antibiotics.

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