The policy on cannabis use in The Netherlands is substantially different from that in many other countries. It is based on the idea that separating the markets for hard drugs and soft drugs pre- vents soft drug users to resort to hard drug use. Over the years so-called coffeeshops emerged. Coffeeshops are alcohol free establishments where the selling and using 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'. Critics of the Dutch drug policy have claimed that the THC-content of nederwiet has increased drastically over the last decades. However, the THC-content of cannabis products as sold in coffeeshops has not systematically been tested. On request of the Ministries of Health and Justice, the potency of cannabis products as sold in coffeeshops in The Netherlands has been investigated since 1999.
∆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 as sold in Dutch coffeeshops. In addition we wanted to know whether there are differences between the cannabis products originating from Dutch grown hemp (nederwiet) and those derived from imported hemp. It is the ninth time that this study has been performed.
It might be that there are differences in potency of cannabis products in different seasons of the year. For that reason, since 2001, every year extra samplings have been done in the month of September. In these extra studies only nederwiet was bought.
The names and addresses of 50 Dutch coffeeshops were randomly selected. For the purpose of this study, 60 samples of nederwiet, 14 samples of foreign marihuana, 10 samples of Dutch hash and 59 samples of hash prepared from foreign hemp were anonymously bought in the selected coffeeshops. In addition, 49 samples of the most potent marihuana product available in the coffeeshop, were bought*10. As a rule samples of 1 gram were bought.
The average THC-content of all the marihuana samples together*11 was 16,0% and that of the hash-samples 17,8%. The average THC-content of nederwiet (16,4%) was significantly higher than that of foreign marihuana (8,5%). Hash derived from Dutch hemp contained more THC (27,6%) than hash originating from foreign hemp (16,2%). The average THC-percentage of nederwiet was the same as last year (16,4 vs. 16,0%). Again, the THC-percentage in foreign marihuana did not differ from the previous samplings. The average THC-percentage of the marihuana samples that were bought as most potent (17,7%) did not differ from the average percentage of nederwiet. The potency of nederwiet bought in September 2007 (15,4%) was not significantly different from
samples bought in January 2008 (16,4%). In the first years of this study, a seasonal difference in the THC-content was found (lower in September), but since two years the potency is the same all year long. There seems to be a stabilization of the potency of nederwiet.
Prices that had to be paid for foreign marihuana were lower than those for any of the other cannabis products. The prices of nederwiet increased significantly during the last two years.
*10 Most potent as indicated by the coffeeshop personnel.
*11 This is not corrected for in terms of relative contribution of number of foreign or Dutch samples.