Considering stimulants (generally, but also specific ones) only work for a portion of people that try it, I find this very unsurprising. The increase isn't that big and probably down to a mixture of disappointment and side effects without the main effects. It's one of the main reasons doctors prescribe different stimulants. I've personally heard every mutation of "This one worked for me but the other one gave me bad…
You'd think by now we would have some way to test the concentration of various things (serotonin, norepinephrine, etc.) in the body BEFORE issuing medications that might modify them, and then measure such concentrations afterwards to get a better idea of what to use, rather than the current "try different things and rely solely on the subjective description provided by the (likely untrained and inarticulate) test sub…
It would be like trying to tracks cars by only observing traffic lights.