I'm certainly no expert, but Tren's potential neurological effects appear to extend well beyond aggression or conventional androgen receptor signaling. Preclinical research suggests it may alter dopamine, serotonin and norepinephrine signaling, contribute to oxidative stress and neuroinflammation, and potentially affect blood-brain barrier integrity through changes in tight-junction proteins such as ZO-1 and occludin.
There are also experimental findings suggesting potential neuronal toxicity. These mechanisms could help explain why users experience changes in irritability, anxiety, emotional regulation, impulsivity and sleep. That said, most of the mechanistic evidence remains preclinical, and the extent to which it translates to humans is still unclear. There's potentially a lot more to Tren's neurological effects than the typical "tren rage" explanation suggests.
ZO-1 and occludin are proteins essential to maintaining the tight junctions that help regulate blood-brain barrier integrity. Preclinical research suggests Tren exposure may reduce their expression, potentially increasing BBB permeability and allowing greater exposure of brain tissue to circulating inflammatory mediators. The implications in humans aren't yet established, but it's an interesting and potentially concerning mechanism.
Basically, Tren clearly crosses the BBB... It's potentially quite fucking potent in this regard.
I'd presume that even at 200 mg of Tren Ace, some individuals could experience bronchial symptoms or changes in exercise tolerance and VO₂ capacity. Has he mentioned experiencing anything along those lines?
So, in closing, I think your friend is either full of shit, running bunk Tren, or isn't actually using it at all because he's too scared to find out what it's really like.
en.wikipedia.org