"While side effects of cannabis are well documented,7 data on human toxicity related to the use of synthetic cannabinoids remains limited. As with other NPS, products sold as synthetic cannabinoids often contain several chemicals in different concentrations, making it very difficult to determine substance-specific effects. Available knowledge on the toxicity of these compounds comes from scientific reports and clinical observations.
"Health-related problems associated with the use of synthetic cannabinoids include cardiovascular problems and psychological disorders,8 and it appears that there may be carcinogenic potential with some of the metabolites of the substances contained in these products.9
"A study published in 2011 on the severe toxicity following synthetic cannabinoid ingestion suggested that JWH-018 could lead to seizures and tachyarrhythmia (irregular heartbeat).10 In a recent review of clinical reports, addiction and withdrawal symptoms similar to those seen with cannabis abuse were also linked to the use of synthetic cannabinoids.11 An analysis of synthetic
cannabinoids in ‘spice-like’ herbal blends highlighted the increasing number of reports on suicides associated with preceding use of these products.12"


UN Office on Drugs and Crime, "The Challenge of New Psychoactive Substances: A Report from the Global SMART Programme" (Vienna, Austria: UNODC Laboratory and Scientific Section, March 2013), p. 5.