I too had been a smoker (for about 5 years) before I was able to give it up. I find that hydration is key to my cognitive function. I can drink up to a gallon of water in a day.
I’m not sure if there is any science or factual claims behind this next bit, but..
I use a supplement called slow-mag. It’s a slow release of magnesium and it seems to help the effectiveness of my current (20mg XR) perscription. Also it should be noted that I haven’t been using it all that long, but I read somewhere that magnesium helps to get rid of the calcium buildup in the brain from the use of dextroamphetamine. (Lamans terms at best) You will definitely want to do your own research.
Best of luck to you.