BACKGROUND The human olfactory system is linked to a channel in the brain and the surrounding environment.After nasal administration,the drug can reach the brain through the following two ways.(1) blood circulation through the BBB to reach the brain.(2) directly through the olfactory region to reach the cerebrospinal fluid or even the brain.Modem studies have shown that the high degree of bioavailability of the certain drugs nasal delivery,and can even be comparable to the injection,but very little amount of drugs into the brain from the nasal pathway.