Conclusions
In addition to the role of herbal products in treatment of a variety of human diseases, natural chemicals are still considered as an inexhaustible source for the development of new active chemotherapeutic agents. Although a great number of natural substances demonstrate therapeutic value in preclinical investigations, their quantity dramatically decreases when they enter the clinical trial stage. It is still difficult for researchers to choose the best in vitro and in vivo models demonstrating the efficacy of natural substances and confirming their inclusion in clinical trials. Alternative in silico and in vitro methods that can considerably reduce the time and expense needed for in vivo studies should be proposed to address these liabilities. The low bioavailability of natural substances usually limits their efficacy. As a result, in addition to the compound’s effectiveness, which should be of great interest, researchers must focus on drug delivery systems that can resolve the compound’s pharmacokinetic problems and the investigation of suitable derivatives offering a number of advantages in terms of biological availability and efficacy.