Ethnopharmacological insights into Symphytum officinale L.: traditional uses, phytochemical composition, therapeutic potential, and clinical-toxicological implications

Symphytum officinale: L. ( S. officinale ), commonly known as comfrey, has been used in traditional medicine for over 2,000 years to treat wounds, fractures, and inflammatory conditions. This review is the first comprehensive ethnopharmacological synthesis that systematically integrates cross-cultural traditional knowledge with the latest evidence on its phytochemical profile, pharmacological mechanisms, clinical efficacy, and toxicological risks. Unlike previous fragmented reviews that addressed only isolated aspects, we followed PRISMA guidelines to analyze selected studies, with a strong emphasis on developing safe, pyrrolizidine alkaloid (PA)-depleted topical formulations that translate the plant’s classic “knitbone” reputation into modern evidence-based phytotherapy. Key bioactive constituents—allantoin, rosmarinic acid, polysaccharides, and lignans—exert anti-inflammatory, tissue-regenerative, and bone-repair effects primarily by inhibiting NF-κB and MAPK pathways and suppressing pro-inflammatory cytokines. Randomized controlled trials demonstrate that topical S. officinale preparations significantly outperform placebo in acute back pain, knee osteoarthritis, ankle sprains, and myalgia, while showing non-inferiority to diclofenac and an excellent safety profile. However, the presence of hepatotoxic PAs (intermedine and lycopsamine) strictly limits internal use. Topical application remains safe owing to minimal systemic absorption. By bridging historical wisdom with rigorous contemporary data and spotlighting PA-depletion strategies, this review offers a balanced framework for safe clinical application and future formulation optimization.