Background: Viral infections remain a major global health challenge due to their high transmissibility, emerging variants, and increasing resistance to conventional antiviral therapies. The search for safe, effective, and affordable antiviral agents has renewed interest in traditional medicinal systems. The Siddha system of medicine, one of the oldest healthcare traditions of South India, utilizes a wide range of medicinal plants with documented antiviral, immunomodulatory, anti-inflammatory, and antioxidant properties. Recent scientific investigations have provided evidence supporting the antiviral potential of several Siddha medicinal plants against a variety of viral pathogens.

Objective: To critically review the current evidence on the antiviral activities of Siddha medicinal plants, elucidate their mechanisms of action, and explore their future prospects in antiviral drug development and integrative healthcare.

Methods: A comprehensive literature review was conducted using electronic databases including PubMed, Scopus, Web of Science, ScienceDirect, Google Scholar, SpringerLink, and the AYUSH Research Portal. Relevant studies published between 2000 and 2025 were screened. Classical Siddha texts, government publications, experimental studies, clinical investigations, molecular docking studies, and review articles reporting antiviral activities of Siddha medicinal plants were included and critically analyzed.

Results: The review identified several Siddha medicinal plants with significant antiviral potential, including Andrographis paniculata (Nilavembu), Tinospora cordifolia (Seenthil), Ocimum tenuiflorum (Tulsi), Phyllanthus emblica (Nellikai), Azadirachta indica (Veppam), Withania somnifera (Amukkara), and Piper longum (Thippili). These plants exhibited antiviral effects against influenza virus, dengue virus, chikungunya virus, herpes simplex virus, hepatitis viruses, and SARS-CoV-2 through multiple mechanisms such as inhibition of viral entry, suppression of viral replication, interference with viral protein synthesis, and modulation of host immune responses. Additionally, many of these medicinal plants demonstrated antioxidant and anti-inflammatory activities that may reduce virus-induced tissue damage and improve disease outcomes.

Conclusion: Siddha medicinal plants represent a promising source of bioactive compounds with broad-spectrum antiviral potential. Their ability to combine direct antiviral activity with immunomodulatory and anti-inflammatory effects supports their traditional use in infectious disease management. Although current experimental and preliminary clinical evidence is encouraging, further standardization, mechanistic studies, pharmacological evaluations, and large-scale randomized clinical trials are required to establish their efficacy and safety. Future integration of Siddha medicinal knowledge with modern drug discovery approaches may facilitate the development of novel plant-based antiviral therapeutics.