Anything that increases dopamine levels has the possibility of causing
oxidative cellular injury due to the primary metabolite of dopamine,
HOVAC or homovanillic acid, and both methamphetamine and amphetamine
cause dopamine release from synaptic vesicles and prevent its reuptake.
In smaller doses, like in Adderall, these drugs do not cause any real
problems because of the body's own antioxidant, glutathione. But in
larger doses, both appear to be neurotoxic.

As to whether this is reversible or not, there are not enough data to
say what happens after a year or two of stopping methamphetamine
because it is so hard to find someone who actually stopped using
completely when doing these types of brain imaging studies. I suspect
that it does come back over time, but this is mere conjecture.

MobiusDick