> This is also why recreational crystal meth [1] is very bad for the brain. Crystal meth overloads the neurons and definitely not equivalent to Rx Ritalin as intelligently prescribed.
"Crystal meth" isn't equivalent to Ritalin (methylphenidate), but it is equivalent to Desoxyn (brand name for methamphetamine), and more or less equivalent to Adderall (d-amphetamine, with a bit of l-amphetamine).
All three drugs are prescribed for a variety of conditions and, in appropriate doses, are safe[0]. The main difference between Desoxyn and Adderall is that the extra methyl group attached to the amphetamine makes it cross the blood-brain barrier more easily, which means that the equivalent doses are smaller (by weight). The metabolic processes and the effects on the brain are virtually identical, though, so it's misleading to draw a line between them and label one as "good" and the other "bad".
The real reason that people think of crystal meth as "bad" is because it's taken in far higher doses recreationally than would ever be prescribed medically, and because it's smoked (not that this is inherently bad, but changing the means of ingestion changes the onset, duration of effects, etc.[1])
[0] At least, to the extent that we can say that any pharmaceutical is "safe"
[1] This is why nicotine gum is frustrating to many smokers, because it takes much longer to absorb.