How to become a cop preferably K9?

ok so here's my question. i am in the army and want to become a police officer when i get out of the army preferably K-9 unit involved in narcotics. i have never done any drugs not even weed. how do i get started? i do have issue's diagnosed with major recurring depressive disorder. i have not taken any medications i dont want to become dependant on them. will that effect my chances?