Avoid like the plague.
Some of them are downright dangerous. I was given some free, and I threw it away after a couple of hours – it clearly was bloody dangerous for my brain. “Annihilation” was the brand, and I could feel it doing that to my brain cells.
I have heard the issue described as “The chemical being a full antagonist for the receptors in the brain.” It’s really completely screwing with a major part of your body’s signalling system, not just tickling it like the natural Cannabinoids [maybe the wrong term, but you what I mean] in a real dried plant.
I know a couple of people who it’s really messed up. One guy can’t smoke anything ever again because he freaks out totally now after using Spice.
AVOID.