Do you know where this information comes from? I did some searching but couldn't find anything.
I'm having problems with it as well, and I wish I could copy something from literature before quoting a person who read something that has been overturned in more recent science. But I was told by an acquaintance of mine who is a bit like a librarian and I really expressed my doubt on the subject myself. If the theory still holds or not, I cannot say, but he had sourced it indeed.
He also had a german chemistry book from around 1900-1910, the entry for mescaline in that was hilarious. It was something like: poisoning is typified by assaulting intense colors or something like that. And a bunch of other things. Formulated like poisoning, but it was evident they were unable to make it sound less than beautiful.
Here is something though!
More than 1,5 grams of mescaline can cause liver-dysfunction and eventually death due to paralyzed bronchial tube.
source
I'd rather have a scientific article as source, otherwise it's admittedly shitty - but still.
Makes you reconsider loading up on mescaline and taking a drug that relies on proper liver function to remain safe (idk... dextropropoxyphene? fck now I'm just thinking out loud indeed), at least.
Yet murple claims on erowid:
Q: I have read somewhere that 1200mg of mescaline can be deadly for humans (respiratory depression, liver damage), which would be three times the amount you need to have a strong trip. Is that true?
A: Any substance can be deadly in high enough quantities, even water. That being said, mescaline is one of the safest drugs known. There have been no verified human deaths from mescaline ever, although K. Trout states that there is one unconfirmed (and unconfirmable) report of a person who died during military experiments with the drug, after receiving a 15 gram dose intravenously (or about 150-200mg/kg).
In experiments with rats, the LD50 for mescaline has been established in the range of 800-1200mg/kg orally.
Considering the human dose of mescaline is around 200-500mg orally, this means you would have to try very hard to take a fatal dose. It would be extremely unlikely to happen accidentally.
I'd have to correct any suggestion about the threshold for serious and significant organ damage to be very low or quite near a fully psychedelic dose and without better source references now place the maximum I would care to take rather between 1000-1500 mg but something I will stick by is that thinking you can just keep on going like with LSD and it's therapeutic I would think again.
Clearly there are problems with accurate numbers and statistics on the subject (acute deaths would be hard to find indeed but contribution to organ damage is of course tricky to distill from statistics) so yeah, I still agree that calling it relatively safe is indeed quite fine...
But again: the sky is not the limit.