Nature reported on September 9, 2026, that the biological boundary separating the brain from circulating blood remains the most formidable barrier in medicine. Small, simple chemical compounds such as paracetamol can cross the blood–brain barrier, but the structure is completely impermeable to larger molecules, including proteins and messenger RNA.
Toxins and pathogens swimming in the blood would wreak havoc in the brain without this separation. That protective impermeability, however, also makes it difficult to treat devastating diseases affecting the delicate organ, because medicines miss their targets when they cannot cross from the bloodstream into brain tissue.
Taiho Oncology, Inc. provided financial support for the drug delivery supplement, which appeared across pages S4 to S7 of Nature volume 657 under DOI 10.1038/d41586-026-02655-6. Nature maintained full editorial independence for the project. The publication points to several earlier delivery studies. It cites 2025 research on pages 1653 to 1663 of Nature Materials volume 24 by C. Wang and colleagues. It also references a 2023 paper by C. Martins and colleagues in Small volume 19, article 2300029, and a 2020 study on pages 69 to 83 of Nature Biomedical Engineering volume 4 by Z. Yang and colleagues.
The supplement outlines several other therapeutic delivery approaches alongside blood–brain barrier research. These include recruiting bacterial couriers to smuggle drugs into cancers, administering nasal vaccines to stop pandemics before they begin, and engineering drugs that treat patients across extended periods. It also highlights the role of patient adherence, noting that medicines do no good if people do not take them.
