https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8068256/
Daraus:
The biggest challenge to drug delivery into the brain is circumventing the BBB [blood brain barrier], which prevents the entry of numerous potential therapeutic agents. While oral administration of the herbs is a common route of administration, there are no clear studies to demonstrate whether the herbal components have access to the CNS from the systemic circulation. Intranasal administration (INA) is non-invasive, rapid, bypasses the BBB, and directly targets the CNS.