Not sure what the rationale is though, in the case of diabetes & hypothyroid, the meds aren't really drugs as such, they're hormone replacements. Something your body ought to make on its own, but isn't.
In Scotland, they do something called Pre-Payment Certificates, so if you do need a monthly medication for any reason, you can basically get a bulk-discount by paying by the year, or per 4 months. Of course, it's a moot point, since in another couple of months, all prescriptions charges will be dropped.