A study of cannabis potency in France over a 25 years period (1992-2016)

Cannabis contains a unique class of compounds known as the cannabinoids. Pharmacologically, the principal psychoactive constituent is Δ⁹-tetrahydrocannabinol (THC). The amount of THC in conjunction with selected additional cannabinoid compounds (cannabidiol/CBD, cannabinol/CBN), determines the strength or potency of the cannabis product. Recently, reports have speculated over the change in the quality of cannabis products, from nearly a decade, specifically concerning the increase in cannabinoid content. This article exploits the analytical data of cannabis samples analyzed in the five French forensic police laboratories over 25 years. The increase potency of both herbal and resin cannabis in France is proved through the monitoring of THC content. For cannabis resin, it has slowly risen from 1992 to 2009, before a considerable increase in the last four years (mean THC content in mid-2016 is 23% compared to 10% in 2009). For herbal cannabis, it has known three main stages of growth (mean THC content is 13% in 2015 and mid-2016 compared to 7% in 2009 and 2% in 1995). The calculation of THC/CBD ratios in both herbal and resin samples confirms the recent change in chemotypes in favor of high potency categories. Finally, the CBN/THC ratios in marijuana samples were measured in order to evaluate the freshness of French seized hemp.