A short introduction to the naturally occurring psychotropic agents including the most important constituents of Cannabis sativa is given. The stereo-specific syntheses of Δ9- and Δ8-THC are described in short. As the synthetic cannabinoid analogues are known to be pharmacologically active, it is worthwhile to discuss the structure-activity relationship of the synthetic cannabinoids in detail. Evidence of the utility of the cannabinoids as potent agents with a wide range of pharmaceutical activity continues to accumulate.