Between 2000 and 2005 the average percentage of Δ(9) -tetrahydrocannabinol (THC) in marijuana as sold in Dutch coffeeshops has increased substantially; the potency of domestic products (Nederwiet and Nederhasj) has particularly increased. In contrast with imported marijuana, Nederwiet hardly contained any cannabidiol (CBD), a cannabinoid that is thought to offset some of the adverse effects of THC. In 2005, the THC content in Nederwiet was significantly lower than in 2004. This study investigates the further decrease or increase of cannabinoids in these cannabis products. From 2005 to 2015 five different cannabis products were bought anonymously in 50 coffeeshops that were selected randomly each year from all coffeeshops in the Netherlands. A total of 2126 cannabis samples were bought, consisting of 664 Nederwiet samples (most popular), 537 Nederwiet samples (supposed strongest varieties), 183 imported herbal cannabis samples, 140 samples of cannabis resin made of Nederwiet and 602 samples of imported cannabis resin. All samples were analysed chemically for their THC, CBD and cannabinol (CBN) content. Between 2005 and 2015, the mean potencies of the most popular and the strongest Nederwiet and of imported cannabis resin were 16.0±4.0%, 17.0±3,9% and 16.5±6.3%, respectively. Imported herbal cannabis (6.5±3.5%) and cannabis resin made from Nederwiet (30.2±16.4%) contained, respectively, less (β=-10.0, P<0.001) and more (β=13.7, P<0.001) THC than imported cannabis resin. Linear regression models were used to study the trends in THC of the different cannabis products over time. A marginal, but significant (P<0.001), overall decline of THC per year of 0.22% was found in all cannabis products. However, no significant difference was found between the five products in the THC linear trajectories across time. Of all the cannabis products, only imported cannabis resin contained a relatively high CBD/THC ratio (median 0.42). The average tetrahydrocannabinol (THC) content of the most popular herbal cannabis products in the Netherlands has decreased slightly since 2005. The popular Nederwiet type still has a relatively high THC to cannabidiol ratio.