Reynoutria ciliinervis (Nakai) Moldenke (R. ciliinervis) root, a traditional Chinese medicine, was found to exhibit remarkable pharmacological properties through a series of comprehensive investigations. Our study commenced with a qualitative phytochemical analysis that identified 12 bioactive compounds within the plant. Subsequently, utilizing ultraviolet-visible spectrophotometry, the methanol extract emerged as the optimal solvent extract, which was abundant in diverse classes of compounds such as carbohydrates, phenolics, steroids, alkaloids, phenolic acids, and tannins. In vitro antioxidant assays underscored the exceptional free radical scavenging, metal ion chelation, hydrogen peroxide scavenging, singlet oxygen quenching, and β-carotene bleaching capabilities of the methanol extract, significantly outperforming other solvent extracts. Further ultra high-performance liquid chromatography–electrospray ionization–quadrupole time of flight–mass spectrometry analysis revealed the presence of 45 compounds, predominantly anthraquinones and phenolics, in the methanol extract. The extract demonstrated robust stability under various conditions, including high temperatures, varying pH levels, and simulated gastrointestinal digestion as well as efficacy in inhibiting the oxidation in edible oils. Acute toxicity tests in mice confirmed the safety of the methanol extract and provided a valuable dosage reference for future studies. Importantly, high-dose methanol extract exhibited a significant pre-protective effect against D-galactosamine-induced liver injury in rats, as evidenced by reduced alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transpeptidase, malondialdehyde levels, and elevated catalase and albumin levels. These findings suggest a potential role for the methanol extract of R. ciliinervis root in treating oxidative stress-related disorders, highlighting the plant’s immense medicinal potential. Our research offers a thorough evaluation of the bioactive components, antioxidant properties, stability, and liver-protecting effects of the methanol extract, setting the stage for deeper investigation and potential clinical applications.
