Panax ginseng C.A. Meyer (Asian ginseng) has long been used in traditional East Asian medicine. It is increasingly incorporated into global herbal supplement and functional food markets, and potentially modulating pathways involved in metabolic regulation, oxidative stress and inflammation. However, this may not translate into consistent clinical efficacy, especially when studies differ in extract type, dose, duration and participant characteristics. As such, this systematic review aims to critically evaluate current evidence on the biological effects and potential health benefits of Panax ginseng. A PubMed search was performed to identify studies up to 31 December 2025. Of the 215 articles identified, 37 were included. The evidence clusters into three main themes: (1) metabolic and physiological regulation, (2) cellular and molecular protective mechanisms, and (3) immune function and host defence. Preclinical studies support the modulation of signalling pathways relevant to metabolic homeostasis, oxidative stress, inflammation and host defence; including AMPK and PI3K/Akt, Nrf2/HO-1, and TLR4/NF-κB/NLRP3-related mechanisms, with metabolomic and microbiomic-related findings suggesting gut microbial biotransformation may contribute to interindividual differences in systemic response. Clinical trials report potentially beneficial effects on glycaemic control, vascular function, stress-related outcomes and selected aspects of cognition; however, the clinical evidence remains difficult to generalise because many studies are small, use heterogeneous preparations, and rely on short-term or surrogate endpoints. Although Panax ginseng appears to be generally well tolerated, a translational gap remains between mechanistic preclinical findings and variable human outcomes, despite its biological plausibility and potential as a complementary intervention.