On a previous thread here about LSD I learned about NBOMe -- it's a hallucinogen that's sold on paper tabs; if a dealer (or their supplier) is unscrupulous they might sell it as LSD. Only problem? Where psychonauts feel comfortable eating mouthfuls of LSD tabs, the difference between noticeable and harmful doses is quite small with NBOMe.

https://en.wikipedia.org/wiki/25I-NBOMe