Don't link it post the study itself. Or an abstract. C'mon now.
I will post the title of the studies that state it is a neurotoxin.
Synthesis, acute toxicities, and antitumor effects of novel 9-substituted β-carboline derivatives
9-Methyl-β-carboline up-regulates the appearance of differentiated dopaminergic neurones in primary mesencephalic culture
Stimulation, protection and regeneration of dopaminergic neurons by 9-methyl-β-carboline: a new anti-Parkinson drug?
The exceptional properties of 9‐methyl‐β‐carboline: stimulation, protection and regeneration of dopaminergic neurons coupled with anti‐inflammatory effects
Synthesis and in vitro cytotoxic evaluation of 1, 3-bisubstituted and 1, 3, 9-trisubstituted β-carboline derivatives
Design of β-carboline derivatives as DNA-targeting antitumor agents
Endogenous β‐Carbolines as Clonidine‐Displacing Substances
This took minimal effort to find these. People might actually listen to the advice you give. If you're able to read studies with a trained eye then do it.
The jist of all the studies so far is that this compound was found to have protective and regenerative effects on dopaminergic cell lines. Dopamine is not even close to our primary neurotransmitter. If you don't have a progressive deadly neuro degenerative disorder such as Parkinson's why would you do damage to the rest of your brain. It makes no sense.