'Spice' and 'K2' herbal highs: a case series and systematic review of the clinical effects and biopsychosocial implications of synthetic cannabinoid use in humans

Cannabis, the most commonly used illicit substance, exerts its primary psychoactive effect via delta-9 tetrahydrocannabinol (Δ(9) -THC) agonism of cannabinoid receptor type 1 (CB1). Some users develop a cannabis use disorder and physical dependence manifested by withdrawal symptoms during abstinence. Hence, there is growing public health concern about increasing use of a new generation of synthetic cannabinoid (SC) agonists (eg, JWH-018, CP 47,497) marketed as natural herbal incense mixtures under brand names such as "Spice" and "K2." Anecdotal reports suggest overlapping effects with marijuana when the mixtures are smoked, however, systematic evaluation of SC-related psychoactive properties and adverse effects is lacking. We conducted a systematic review of published reports on SC clinical effects in humans. Most highlight potential toxicity such as acute anxiety and psychosis. In addition, we carefully document three cases in which experienced marijuana users meeting criteria for cannabis dependence with physiologic dependence smoked SC products regularly. The SC mixture effects were reportedly similar to marijuana and well tolerated. The individuals all reported that SC product use effectively alleviated cannabis withdrawal. Biopsychosocial factors associated with SC initiation and usage by the cases help to shed light on psychopharmacologic, clinical, and public health aspects of SC product consumption.