4 years is a good time for tolerance to build for an amphetamine. It's good that you are not on the max dosage. That means you can increase the dosage for the dextroamphetamine to have more of an effect.

You might have to take a break from it for a while. 5-6 months (sorry ya I know it's long but that's being generous as a good 2 years would be good from using it chronically for 4 years). I'm not sure. Maybe I could be thinking about the people that built a tolerance after taking it for 10-15 years so it could be shorter.

And yes, I know you would probably feel dosey and spacey, irritable, agitated, mind racing etc.. Which would be worse than before you started taking it (if it in fact is tolerance to the drug) but there is no use in taking something that doesn't work anymore.

You could also try magnesium daily. You can get this from the drug store or a health food store. Speed junkies use it to decrease their tolerance which is why people with ADHD are recommended to take it with their meds, especially with Ritalin. I'm not sure which type of magnesium it is I'll check it out. I'm going to do the same thing. It's supposed to make stimulants more effective and clears out your brain when it wears off at the end of the day (because yknow.. Stimulant molecules are actually small zombie parasites that feed from brain flesh).

There was something else I was about to say but I forget..