Through extensive study, scientists have found that compounds that are very small and/or fat-soluble, including antidepressants, anti-anxiety medications, alcohol, cocaine, and many hormones are able to slip through the endothelial cells that make up the blood-brain barrier without much effort. In contrast, larger molecules, such as glucose or insulin, must be ferried across by proteins. These transporter proteins, located in the brain's blood vessel walls, selectively snag and pull the desired molecules from the blood into the brain.
Size of glucose molecule (open chain form) Value. 1.5 nm
