Not sure if this new wave of synthetic shit has been mentioned, mostly compounds intended to act like weed, but from experience I would caution people against them. Especially if you plan on skipping over the pricey blends like K2, Spice, etc.. to get the actual active compounds like JWH-018, etc.. which are dirt cheap, and super effective. SCARY effective if used irresponsibly.
I have a high tolerance to pretty much every mind altering substance I've ever tried, which I don't say as a boast.. but to illustrate how scary these chems are. I could smoke the best weed all night and only get mildly high. Hell, when I go to the dentist they have to double the dose of novacain and even then I only get slightly numb and can feel everything.
So when I say that just a few grains of JWH-018 or MDPV were enough to make me fear for my life and sanity, it should mean something. Stay away from this shit if you care about yourself at all. I feel really stupid for trying several of these and taking as long as I did (2 months) to finally come to the conclusion that it's playing with fire.
Simply put, there's not enough research and knowledge about these checmicals yet. For all we know, five years from now MDPV could be considered ten times more deadly than heroin. You're better off sticking to pot... and probably even coke, crack and heroin: at least if you od on those, any medical professional will have training on how to deal with it. Mention JWH-018 or MDPV to most doctors and you'll get a blank stare.