Biological barriers to precision medicine applications significantly challenge its effectiveness. Genetic variability among individuals leads to differing responses to treatments, making it difficult to predict outcomes. Additionally, the complexity of diseases, especially those involving multiple genes and environmental factors, complicates the development of targeted therapies. Epigenetic modifications and gene-environment interactions further obscure the relationship between genotype and phenotype, limiting the precision of treatments. Moreover, the tumor microenvironment in cancer and the blood-brain barrier in neurological diseases pose significant obstacles to drug delivery. These barriers underscore the need for continued research and innovation to overcome the limitations of precision medicine.