In cannabis resin, the THC concentrations tripled from 7·6% (IQR: 4·2 to 11·7%) to 24·1% (IQR: 16·5 to 27·5%), as suggested by data provided by 20 countries between 2010 and 2019 (see also Figure 5). At the country level, regression models found no significantly declining THC concentrations in resin in any country but significantly increasing THC concentrations were present in eight countries. In Austria, Germany, Portugal, Italy, and Estonia, annualized change rates ranged between +0·8 and +1·5 percentage points. In France, Sweden, and Luxembourg, THC concentrations in resin rose at an annual rate of 2·3 to 2·5 percentage points.
