Synergistic and Additive Effects of Herbal Medicines in Combination with Chemotherapeutics: A Scoping Review

Background: Natural products are increasingly gaining interest as potential new drug candidates for cancer treatment. Herbal formula, which are combinations of several herbs, are primarily used in East Asia and have a long history of use that continues today. Recently, research exploring the combination of herbal formulas and chemotherapy for cancer treatment has been on the rise. Methods: This study reviewed research on the co-administration of herbal formulas and chemotherapy for cancer treatment. The databases PubMed, Embase, and Cochrane Library were used for article searches. The following keywords were employed: “Antineoplastic agents,” “Chemotherapy,” “Phytotherapy,” “Herbal medicine,” “Drug synergism,” and “Synergistic effect.” The selection process focused on studies that investigated the synergistic interaction between herbal formulas and chemotherapeutic agents. Results: Among the 30 studies included, 25 herbal formulas and 7 chemotherapies were used. The chemotherapy agents co-administered included cisplatin, 5-fluorouracil, docetaxel, doxorubicin, oxaliplatin, irinotecan, and gemcitabine. The types of cancer most frequently studied were lung, breast, and colon cancers. Most studies evaluating the anticancer efficacy of combined herbal formula and chemotherapy treatment were conducted in vitro or in vivo. Discussion: Most studies reported synergistic effects on cytotoxicity, apoptosis, and tumor growth inhibition. These effects were found to be associated with cell cycle arrest, anti-angiogenesis, and gene expression regulation. Further studies leading to clinical trials are required. Clinical experiences in East Asian countries could provide insights for future research.