In Vitro Antineoplastic Effects of <i>Zataria multiflora</i> : A Systematic Review of Mechanisms, Selectivity, and Synergy

ABSTRACT Zataria multiflora (ZM), a plant with recognized ethnomedicinal properties, harbors a spectrum of bioactive compounds demonstrating cytotoxic potential against various cancer cell lines. However, the absence of a systematic synthesis of individual research efforts has significantly impeded the translation of promising in vitro findings into rigorous clinical investigations. This study aims to systematically review and synthesize the current evidence regarding the in vitro anticancer effects of ZM. A meticulous systematic search, adhering to the PRISMA guidelines, was executed on September 17, 2025, across major scientific databases, including Web of Science, Medline, Scopus, Embase, Magiran, and Google Scholar. The search strategy incorporated relevant keywords, Medical Subject Headings (MeSH) terms, and their Persian equivalents to ensure comprehensive coverage. Retrieved articles underwent rigorous screening to identify eligible studies, and literature saturation was confirmed through a manual review of the reference lists of the selected publications. From an initial pool of 107 articles retrieved from databases as well as 52 articles identified through manual searching, a total of 29 papers were included. We reviewed the cytotoxicity and safety of ZM across 24 cancer cell lines (derived from 13 neoplastic diseases) and six normal cell types. While 17 studies explored the anticancer effects of ZM, 8 investigated its nanoscale formulations, and 4 combined both methods. ZM consistently demonstrated significant pro‐apoptotic effects in cancer cell lines, a phenomenon not observed in normal cells, highlighting its selective cytotoxicity. Previous studies have also reported synergistic effects between ZM and conventional anticancer agents, including doxorubicin, as well as with radiotherapy. A prominent mechanism of action identified was cell cycle arrest (in G1, G2, or S phases) in cancer cells. Preliminary in vitro evidence suggests the promising role of ZM in inducing apoptosis, prompting cell cycle arrest, and reducing proliferation in various cancer cell models. However, to conclusively establish the efficacy and safety of ZM in clinical settings, further research employing advanced models, such as spheroid‐based cell cultures, in vivo animal models, and well‐designed clinical trials, is indispensable.