I remember something like this in my medical pharmacology course. You can get it injected i.m. (intramuscular) and due to the med's properties and the area where it is injected, it'd slowly be released and you can get monthly injections. They have this for other disorders also. I have no clue on the cost of this but I do know i.m. injections are said to be quite painful and to be done ideally in a hospital or possibly doctor's office.

Not all drugs can be injected this way, as some will just stay in the muscle tissue and sometimes crystallize, such as digoxin (heart medication). I have to go to class (for human anatomy and physiology then genetics) so I can talk more about it later.