Although this happened well over two months ago, word of mouth has not really spread this news too far. In November of 2008, German pharmaceutical company THCPharm speculated that the reason reported effects of smoking the "legal herbal blend" found in Spice products (Spice Gold, Spice Diamond, etc.) were similar to marijuana was because they contained a synthetic cannabinoid.
Note: Cannabinoids are molecules that bind to cannabinoid receptors in the brain (CB1, CB2, etc.) The "original cannabinoid" is delta-9-tetrahydrocannibinol, better known as plain ol' THC, which is a partial agonist on both CB1 and CB2 receptors. )
The reason the company was concerned, I am willing to guess is because Spice products have been the only 'legal high' that has recieved mostly positive reviews. Most other "legal highs" are attributed to the placebo effect or crappy herbs that give the user nothing but a headache. Many users reported that smoking Spice "got them ripped"... i.e. color enhancement, tactile enhancement, heavy eyes, increased appetite, etc. These are all trademark signs of the activation of cannabinoid receptors.
Well, anyways, on December 15, 2008, the company confirmed it's suspicions: three different versions of Spice products contained a synthetic cannabinoid and research chemical JWH-018. While not very structurally similar to THC, JWH-018 is indeed a potent cannibinoid. Ingesting JWH-018 is not believed to give false positives for THC on drug tests, so it can be considered a viable alternative to marijuana for those who need to "stay clean" for a test.
JWH-018
Following the company's discovery, Austria, Germany, Switzerland, and the Netherlands have all banned the sale of spice and JWH-018 itself. However, Spice as well as JWH-018 as a research chemical remain "legal" elsewhere. However, in the United States, people have said the drug would be classified as illegal under the Federal Analog Act. Since JWH-018 is not structurally similar to THC it remains legal. The similarity in effects, however, I believe will lead to its eventual banning in the US. (Once the media hops on the Spice bandwagon). Until then, stock up on Spice and order some JWH-018 (not for consumption of course) from your friendly local research chemical vendor!