The point of the magnesium is to replace the gabapentin as it affixes to the receptors so they do not miss the gabapentin. You can easily take 500 mgs a day. If you are mag deficient, you could take more. Any change needs to be maintained for a reasonable time to allow the blood levels to establish.

I suggest you continue to take the mag 3 times a day even if you do not notice a difference. Your brain needs it anyway.

Your struggle to taper off gabapentin is unique. I wonder if there is something else at play.

Are you being treated for depression ?

Gabapentin is NOT an antidepressant. Please don't consider it a treatment for depression.