How long does mescaline stay in your system?

It is Very rare and expnxive to test for. It would be extremely unlikely to be tested for it, unless you were being tested specifically for mescaline alkaloid fro some reason maybe for certain suspicion of ingesting mescaline. But in that rare case it is somewhat contreversial but most all have settled on 3 anywhere between 3 and 7 days. I hope this helps and if you have any more questions involving hallucinogens feel free to ask.

Mescaline stay in your system: up to 90 days in hair, 1-3 days in saliva, 2-3 days in urine, 1 day in blood

Source: detoxtime4drugs.com