Synthetic Marijuana known as "fake weed", common brands include Spice, K2, Mr. Nice Guy. The chemical products mimic the effects of cannabis but without the active ingredient THC. Even though synthetic marijuana can cause hallucinations, these are over-the-counter products and they are marketed as herbal incense or as potpourri. These drugs evade laws because their active ingredients are not regulated. When certain chemicals get banned, new versions emerge to continue the cycle. These chemicals are: JWH-018, JWH-073, HU-210. Some banned versions include: JWH-018, JWH-073, CP-47,497, JWH-200. At least 15 states have banned their use. The JWH series of chemicals act as a full agonist to the Endocannabinoid System, unlike THC, which is a partial agonist. As such, users experience dependence, tolerance, and withdrawal more severely than marijuana smokers. In addition, the U.S. Navy has a zero tolerance policy on their consumption. JWH abbreviation is for Professor John W Huffman, he created the chemical. He is quoted as saying "People who use it are idiots." 
At the moment, "fake weed" does not show up in drug tests. There are many instances of teenagers going to the hospital after being overcome by severe reactions to these chemicals when smoked.