Synthetic cannabis, also known as K2 or Spice, is a psychoactive designer drug developed from natural herbs and synthetic chemicals that simulate the pleasurable effects of cannabis. There is controversy about calling Spice and K2 synthetic cannabis because the ingredients contained in these products are mimics, not duplicates of THC.

When synthetic cannabis blends first hit the market in the early 2000s, it was believed that they produced their effects through a mixture of legal herbs. Laboratory analysis showed that this was not the case, and that they in fact contained synthetic cannabinoids that act on the body in a similar way to cannabinoids naturally found in cannabis, such as THC. A large and complex variety of synthetic cannabinoids, most often cannabicyclohexanol, JWH-018, JWH-073, or HU-210, are used in an attempt to avoid the laws that make cannabis illegal, making synthetic cannabis a designer drug. It has been sold under various brand names, online, in head shops, and even at some gas stations.

Though its effects are not well-documented yet, extremely large doses may cause negative effects that are in general not noted in cannabis users, such as increased agitation and vomiting. Professor John W. Huffman, who first synthesized many of the cannabinoids used in synthetic cannabis, is quoted as saying, “People who use it are idiots. You don’t know what it’s going to do to you.” A user who consumed 3 g of Spice Gold every day for several months showed withdrawal symptoms, similar to those associated with withdrawing from the use of narcotics. Doctors treating the user also noted that his use of the product showed signs associated with addiction. Another case has been reported where a user, who had previously suffered from cannabis-induced recurrent psychotic episodes, suffered reactivation of his symptoms after using Spice. Psychiatrists treating him have suggested that the lack of an antipsychotic chemical, similar to cannabidiol found in natural cannabis, may make synthetic cannabis more likely to induce psychosis than natural cannabis.