Abstract
The blood-brain barrier (BBB) maintains homeostasis by blocking toxic molecules from the circulation, but drugs are blocked at the same time. When the dose is increased to enhance the drug concentration in the central nervous system, there are side-effects on peripheral organs. In recent years, genetic therapeutic agents and small molecules have been used in various strategies to penetrate the BBB while minimizing the damage to systemic organs. In this review, we describe several representative methods to circumvent or cross the BBB, including chemical and physical strategies.