In recent years, studies on evaluation of the therapeutic and toxic activity of herbal medicinal products became available and popular. The advances in modern biotechnology have led to discovery of many new active constituents. However, it is a constant challenge to establish the pharmacological basis for efficacy and safety of herbal medicinal products. A better understanding of the effects and bioavailability of phytopharmaceuticals can help in discovering suitable and rational therapies. In this review, we present the bioavailability studies in immune system that has been conducted for some of the more important or widely used phytopharmaceuticals. Furthermore, various new drug targets worthy of using for drug development in immunomodulating herbal medicine area and their regulatory mechanisms are also discussed. Adverse effects, drug interactions, and contraindications are also discussed which show that caution should be exercised when combining phytopharmaceuticals with chemically derived pharmaceutical components.
