As I have yet to get any decent sleep still coming up on the 3 month mark of my fall I tried a half of a 600 mg gabpentin pill and did not notice any effect at all

How long do you have to be taking it for it show any effect? couple days? perhaps a week? is it possible I don't respond to medication like I should because of the injury?

I ask this because I have tried numerous different meds that seem to have no effect whatsoever on me and some of them Ive tried pre injury that did work