It is also aimed at limiting the amount of THC in soft drugs as current high dosages are believed to cause psychosis in some people. Amsterdam, which has 166 coffee shops, may have played a pivotal role in the experiment, the Parool states.

In a letter to justice minister Ferdinand Grapperhaus and health minister Bruno Bruins, Halsema says that although Amsterdam is in favour of changes to the drugs policy she does not agree with the stipulation that all coffee shops must participate in the experiment. Back door ‘All Amsterdam coffee shops will have to get rid of their illegal suppliers in one go.

This may create a ‘back door’ problem,’ the mayor is quoted as saying. She also objected to the narrow choice allowed under the rules of the experiment – some 10 to 14 marijuana varieties and five to ten hash varieties. Limiting the number ‘increases the risk of cannabis being sold on the street with all the public order problems this will bring,’ the mayor wrote.

One option would be to allow coffee shops to sell their present supply of cannabis along with the new regulated kind for a time, the mayor said in her letter. ‘It will have to made clear to coffee shop owners that after a transition period only the sale of regulated cannabis will be permitted,’ the paper quotes her as saying. The government’s plans have also been cricitised by the Council of State, the government’s most important advisory body.