brain damage/changes from nicotine?
There's an oft-parroted claim that nicotine changes the juvenile brain, or causes irreperable damage in its development. This of course is bunk, based on misrepresenting rodent studies.
The human brain in 14-19 year olds is nothing like that of rats or mice in their
equivalent "adolescent" stage (4-12 weeks old).
And if nicotine had such lasting effects on the human brain, "would we not have seen it?" (Tobacco had been around for a century.)
- Myth #6: The nicotine in JUUL causes brain damage in teenagers
- Q4.6: Does nicotine damage the developing adolescent brain?
- Vaping: what people are getting wrong | The Economist
- Youtube: Is Nicotine harmful to developing brains?
- SRNT15 class it a "speculative" claim
nicotine == poison
The origin assumption is certainly that nicotine is a plant neurotoxin for insects. Which of course has much less implications for humans, where it acts more like a nutrient/hormone. (When oxidized as nicotinic acid; it's also called niacin, formerly known as a vitamin b3 form [term not used anymore]).
nicotine == heroin
The hyperbolic heroin comparison from 1986 notwithstanding, that's not to say that nicotine couldn't induce an addiction by itself (even isolated from tobacco).
|promote substance affinity||fairly plausible🟩|
|changes the brain||get outta here🟥|
But the implication that it changes the human brain, even for individuals where it potentially promotes other substance use, is still a bit farfetched. 
media scare phrases
- "nicotine = brain poison🟥" (TFCA/flavorshookkids, PR agency)
- sci-fi brain worms🟥 (FDA, CTFK?)
- "harm adolescent brain development🟥" (CDC-OSH)
- "Studies in rats🟧 have shown that chronic nicotine exposure during adolescence can diminish cognitive functions" (TI), and straight up lies in some more blatant tweets🟥.