Excuse me, I seem to have misrepresented the information we have.
There is a chance for this to be severely neurotoxic due to my experiences with high IV doses and several peoples' reports of amnesia, including mine. This can be ignored, but I see it as indicators of neurotoxicity and I'm gonna eat a broom if I am mistaken about that. Just my gut feel, but the indicators are there. I consumed the substance throughout months and had weeks off during which my neurogenic pain, paresthesia and hypesthesia would go into remission, but 2-3 500mg doses would bring it back on within hours.
It's typical for a substance to become toxic after a certain threshold dose, eventhough some substances' toxicity scales down to low doses while showing more severe clinical manifestations at higher doses. Severe changes in perfusion around nerves can lead to cell death, so there are other ways for this to exhibit neurotoxic effects than causing cell death through a more direct mechanism, eventhough the apparent 'caustic' properties (one person reported damage on plastic) seem to indicate some form of direct tissue damage. So did my reactions at the injection sites, but then again I have developed a needle fixation which sometimes causes me to compulsively poke myself many hundred times in a sitting.
My odd and inconsistent doses represent my changing tolerance to stimulants and the fact that I consumed different substances in different episodes of my journey into stimulant abuse. Amphetamine phosphate (very clean salt) became really weird at 600mg in 2 consecutive intravenous doses spaces a couple of hours apart at a point in time when I had no acute stimulant tolerance. I couldn't always do these doses, it really feels like I'm knocking on heaven's door every time. So do 500mg 3F-P. Oh and I've never done meth because it's unhealthy!

Stimulant free for more than 6 weeks now, yay.
EDIT: I not once said there was a comedown. I don't get comedowns off stimulants except for cocaine which is dominated by cravings and is limited to the hours when I still have a lot of it in my blood. A comedown is not necessarily a sign of neurotoxicity, polyneuropathia and amnesia are much stronger indicators in this respect.