Which mechanism limits the effectiveness of drug delivery across the blood-brain barrier at the molecular level?

💡 Explanation

When drugs diffuse through the blood-brain barrier, efflux transporter activity pumps hydrophobic molecules back into the bloodstream, lowering drug concentration in the brain due to ATP-driven transport. Therefore, efflux pumps limit effectiveness, rather than swelling, degradation or receptor downregulation, which are controlled through separate pathways.

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