Generally speaking, when I researched that sort of thing, I ended up coming to the conclusion that there hadn't been any definitive studies of anything that didn't actually diminish the effect of the amphetamine. Some of them quite definitely reduce tolerance, but they reduce how much effect the drug has as well, and I couldn't find any information on whether the reduction was proportional, greater, less -- you get the point. Lack of info.I'm wagering memantine would be no different, but do let us know if you try it and disagree.