The research group behind the paper looks reliable, they have a publication record in the area and while it's surprising they can detect metabolites (and surprising that brains were preserved from the 1600s) they seem to have done a lot of detailed work, here's some of their other related work (they also found cannabis residues in some of their material):

"Forensic toxicological analyses reveal the use of cannabis in Milano (Italy) in the 1600's (2023)"

https://www.semanticscholar.org/paper/Forensic-toxicological...