Since the nineteen seventies the policy on cannabis use in The Netherlands has substantially been different from that in many other countries. It is based on the idea that separating the markets for hard and soft drugs prevents cannabis users to resort to hard drug use. Over the years so-called coffeeshops emerged. Coffeeshops are alcohol free establishments where the selling and the use of soft drugs is not prosecuted, provided certain conditions are met. Many of the cannabis products sold in these coffeeshops originate from Dutch-grown grass called ‘nederwiet’. On behalf of the Ministry of Health, Wellfare and Sports we investigate the potency of cannabis products as sold in coffeeshops in The Netherlands.

∆9-Tetrahydrocannabinol (THC) is the main psychoactive compound in marihuana and hashish. The aim of this study is to investigate the concentration of THC in marihuana and hash (=cannabis resin) as sold in Dutch coffeeshops. In addition we examined whether there are differences between the cannabis products originating from Dutch grown hemp (nederwiet) and those derived from imported hemp. This is the twelfth consecutive year that this study has been performed. Apart from THC, the content of two other cannabinoids, cannabidiol (CBD) and cannabinol (CBN), are measured.

The names and addresses of 50 (out of a total of 666) Dutch coffeeshops were randomly selected. For the purpose of this study, 65 samples of nederwiet, 19 samples of imported marihuana, 9 samples of Dutch hash and 56 imported hash samples were anonymously bought in the selected coffeeshops. In addition, 49 samples of the most potent (herbal) marihuana product available were bought. As a rule samples of 1 gram were bought. Samples were bought anonymously.

Traditionally hash contains more THC than marijuana. The average THC-content of all the marihuana samples together was 15,3% and that of the hash-samples 16,5%. The average THC-content of nederwiet (16,5%) was significantly higher than that of the imported marihuana (6,6%). The average THC-percentage of the marihuana samples that were bought as most potent (17,0%) did not differ from that of the most popular varieties of nederwiet (16,5%). Hash derived from Dutch hemp contained more THC (29,6%) than hash originating from foreign cannabis (14,3%). The average THC-percentage of nederwiet was lower in 2011 than in 2010 (16,5 vs. 17,8%), but this difference was not statistically significant. The THC-percentage in imported hash was significantly lower than the year before (14,3% in 2011 versus 19,0% in 2010).

The full report (in Dutch), THC-concentraties in wiet, nederwiet en hasj in Nederlandse coffeeshop 2010-2011, is available here.

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