A Review of the Properties of Clinically Evaluated Plant-Derived Agents in the Treatment of Respiratory Infections.

2026-05-12
Nutrients 18(10)
- Alexandra S Alexandrova
- Vasil S Boyanov
- Liliya Y Boyanova
- Raina T Gergova

PubMed: 42196994
DOI: 10.3390/nu18101534

Study Design

Type: Review
Sample size: n = 94
Methods: We conducted a literature search using the PubMed database focusing on clinical studies of plant-derived agents in upper and lower RTIs. PRISMA-based reporting elements were used only as a guiding tool for comprehensibility of the literature search.
Funding: Unclear

Rigorous Journal

Background: The use of plant-derived agents is a common approach in integrative care for respiratory conditions. However, the evidence of clinical trials has not yet been comprehensively presented. Aim: To summarize the antibacterial, antiviral, immunomodulatory, antioxidant, and expectorant properties of Echinacea spp., Pelargonium sidoides, Hedera helix, Thymus vulgaris, Althaea officinalis, Sambucus nigra, Zingiber officinale, and Curcuma longa, and to evaluate the evidence level from clinical trials (CTs) involving these agents in patients with respiratory tract infections (RTIs). Methods: We conducted a literature search using the PubMed database focusing on clinical studies of plant-derived agents in upper and lower RTIs. PRISMA-based reporting elements were used only as a guiding tool for comprehensibility of the literature search (Reporting Items for Systematic Reviews and Meta-Analyses guidelines). Results: A summary and structured overview of the properties of these most-cited plant-derived agents in the literature, in the context of RTIs, was provided. A total of 94 reports met the eligibility criteria and were included in our review. Of these, 66 reported randomized and placebo-controlled trials investigating the efficacy and tolerability of these adjuncts in patients with RTIs. The non-randomized and uncontrolled trials were 22. Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents. Robust evidence available was found for Echinacea spp., Pelargonium sidoides, Sambucus nigra, Curcuma longa and Zingiber officinale. Conclusions: Regarding other plant-derived agents reported in the traditional medicine for the treatment of RTIs, further research is needed to clarify the evidence gaps.

Research Insights

Echinacea→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Echinacea→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Elder→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Elder→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
English Ivy→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
English Ivy→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Geranium→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Geranium→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Ginger→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Ginger→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Marshmallow→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Marshmallow→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Thyme→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Thyme→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Turmeric→Reduced Duration of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small
Turmeric→Reduced Severity of Respiratory Tract Infection
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Effect
Beneficial
Effect size
Small

Adverse Events Reported

Thyme→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
Ginger→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
Marshmallow→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
Turmeric→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
Elder→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
Geranium→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
English Ivy→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported
Echinacea→Overall tolerability
Sufficient evidence to be regarded as an appropriate treatment to reduce the severity and duration of RTIs was found for all discussed plant-derived agents.
Finding
Reported