While this barrier's impenetrable quality is good for regular function, it's a real pain when doctors are trying to treat diseases. About 95 percent of drugs administered through typical means (pill, injections, enemas, patches) don't have any function in the brain. So doctors have been looking for ways to penetrate it so that medications can treat the brain without permanently damaging the barrier, which would leave the brain vulnerable to infection or chemical imbalance. The researchers have had a couple of leads—they found that certain tiny molecules, such as alcohol and nicotine, can penetrate the barrier, so they thought maybe they can just make drug molecules small enough. Others found that different drug delivery mechanism—enzymes, or ultrasound, or nanoparticles—might make the barrier passable.