> I understood Ritalin to have mild neurotoxic effects, but Adderall et al to be essentially harmless.

There is no conclusive research on humans, but you have these backwards. Ritalin (methylphenidate) is thought to have less risk for neurotoxicity than Adderall (amphetamine). Amphetamine enters the neuron and disrupts some internal functions as part of its mechanism of action, while Ritalin does not.

Both drugs will induce tolerance, though. The early motivation-enhancing effects don't last very long.

There are also some entertaining studies where researchers give one group of students placebo and another group of students Adderall, then have them self-rate their performance. The Adderall group rates themselves as having done much better, despite performing the same on the test. If you've ever seen the confidence boost that comes from people taking their first stimulant doses, this won't come as a big surprise. These early effects (euphoria, excess energy) dissipate with long-term treatment, but it fools a lot of early users and students who borrow a couple pills from a friend.