A lot of doctors use meds for things that are not neccessarily what the drug companies intend them for.

Sometimes the drug companies will remarket them for that purpose, sometimes not.

Example would be Topamax, which was originally an epilepsy drug, found as a fantastic migraine preventative and remarketed that way, also works very well as a mood stabilizer - I'm not sure if it's marketed that way too but a lot of Pdocs prescribe it.

Even Trazadone, which was originally an antidepressant, is prescribed a lot of times just to help with sleep.

Each Pdoc has their own reasons for prescribing what they do i guess...if you feel good then I wouldn't sweat the label so much.