The Role of Nutraceuticals in Chemoprevention and their Therapeutic Effects when Used in Combination with Synthetic Drugs

Recently, increasing attention has been directed toward nutraceuticals, natural substances extracted from plants, fruits, or cereals. These compounds are well-known for their antibacterial, anti-inflammatory, antioxidant, and antitumor properties, with the latter being the primary focus of this review. The use of nutraceuticals, both as standalone treatments and in combination with standard chemotherapy, has been extensively studied through in vitro, in vivo experiments, and clinical trials for the prevention and treatment of various types of cancer, including breast, colon, pancreatic, prostate cancers, and leukemia. Findings from these studies emphasize the benefits of nutraceuticals in improving patient compliance and mitigating the adverse effects of conventional drugs. Specifically, the combination of nutraceuticals with chemotherapy allows for reduced dosages of synthetic drugs, thereby lessening their often-severe side effects. In this review, we explore the diverse mechanisms of action underlying the antitumor activity of key nutraceuticals—including curcumin, resveratrol, tocotrienols, ursolic acid, fisetin, gambogic acid, catechins, silibinin, berberine, emodin, piperine, deguelin, garcinol, plumbagin, zerumbone, and ginger. Furthermore, we summarize the most significant outcomes from clinical trials investigating these compounds. The clinical studies addressed various aspects of treatment, such as efficacy, safety, maximum tolerated doses, potential adverse effects, and patient compliance. The majority of the findings highlight the positive impact of combining nutraceuticals with chemotherapy, demonstrating enhanced therapeutic outcomes in anticancer treatments.