The blood brain barrier, it can be very picky about who [or what] can come in.
Ever wonder why you don’t see too many illnesses that affect the brain directly? You can give your head a nice pat and congratulate the blood brain barrier for keeping the bad out and letting the good in. Unfortunately the blood brain barrier can be, well a barrier, or more like a bouncer– especially when it comes to new drugs that could potentially help treat issues with the brain.
The blood-brain barrier helps that finicky brain of yours maintain the delicate environment that it needs to thrive. There’s just one problem: The barrier is so good at what it does, it won’t let medicines pass through. Like most things with the brain, we don’t know enough about it to control it for our benefit.