Changes in the Composition of Cannabis From 2000-2017 in Denmark: Analysis of Confiscated Samples of Cannabis Resin

Globally, recent studies report increases in Delta-9-tetrahydrocannabinol (THC) concentration in seized samples of cannabis for human consumption. This is important, because use of cannabis with a high concentration of THC has been linked to a number of adverse health outcomes. The objective of this study was to assess recent changes in the composition of seized cannabis resin in Denmark by (a) examining THC concentration in samples from Danish forensic laboratories from 2000 to 2017 (N = 430) and (b) examining cannabidiol (CBD) concentration and the THC: CBD concentration ratio in samples from the forensic laboratory in Western Denmark from 2008 to 2017 (N = 147). Cannabis resin samples were analyzed using a gas chromatographic analysis with flame ionization detection quantifying the total THC and CBD concentration. Results showed that the THC concentration increased 3-fold from 2000 (mean: 8.3%) to 2017 (mean: 25.3%). Significant increases occurred in all areas of Denmark. After 2011, we found a dramatic increase in cannabis resin samples with high THC concentration and the near disappearance of cannabis resin samples with medium-and low THC concentration. Furthermore, the THC: CBD concentration ratio increased significantly from 1.4 in 2008 to 4.4 in 2017. Whereas THC concentration increased, CBD concentration remained stable at similar to 6%. In conclusion, the THC concentration of cannabis resin, and THC: CBD concentration ratio, have increased dramatically in Denmark, potentially leading to higher risk of harm to users. Policymakers, treatment professionals, and educators should be aware of this change. Public Health Significance Based on seized cannabis resin samples from 2000 to 2017, we observe a threefold increase in THC concentration and a rise in THC: CBD concentration ratio, suggesting that cannabis users may be exposed to higher doses of THC, which may carry a greater risk. Observed trends are strikingly similar to trends reported in France, suggesting that the emergence of new, resin products with higher THC concentration has widely penetrated European markets, including Scandinavia. Policymakers, treatment professionals, and educators should be aware of this change.