I recommend staying away from street dealers. There was a huge influx of NBOx compounds sold as LSD blotters since 2017 (apparently there was a global LSD shortage around that year, and IIRC they're cheaper to produce?) Their safety profile is not well-understood but it looks like it's riskier than the (very safe) LSD due to their vasoconstriction effects, and fatal doses aren't that high compared to active doses, unlike LSD which has a huge buffer.

Also people tend to describe their trips as being subjectively less pleasant.

And please, if you have to resort to dealers, invest in a cheap testing kit. You might be lucky and find a nearby non-profit that can not only do a cheap reactive test, but also a purity test.

Stay safe out there.

EDIT: Sibling comments also mention compounds like 1P-LSD sold online. I'd still test those even if bought from reputable vendors.

Anyways, their safety profiles aren't really that well understood either. They're suspected to be just metabolized into LSD and therefore pretty safe, but they're very new (~2015) and after all they're research chemicals (or rather, not-yet-researched chemicals). In comparison LSD had been known for decades and it's pretty well understood.

I guess this is what prohibition leads to...