shunt 135 external region 122 is substantially less permeable to the drug or drug solution in some embodiments external region 122 is flexible rigid or semi rigid external region 122 may comprise a glass polymer rubber ceramic paper cotton or metal material external region 122 can be monolithic molded pressed or machined material or can comprise a woven substrate including a tightly woven substrate in some embodiments more permeable region 130 is substantially more permeable than external region 122 or in some embodiments comprises a region with substantial permeability in some embodiments substantially more permeable means that more permeable region 130 allows diffusion from drug reservoir 140 at a rate within a range of rates such that neither too much or too little drug is delivered from device 100 in some embodiments too much drug being delivered means that the amount of drug delivered causes the drug concentration to exceed the maximum therapeutic dosage in some embodiments too much drug being delivered means that the amount of drug delivered causes the drug concentration to be high enough that the drug 39 s toxic side effects substantially outweigh the drug 39 s beneficial effects as measured by an ordinarily skilled artisan in some embodiments too.