PARIS — Amsterdam’s 220 coffee shops, where marijuana and hashish are openly sold and consumed, will remain open next year in spite of a new Dutch law meant to reduce drug tourism, the city’s mayor said in an interview published Thursday.

The mayor, Eberhard van der Laan, told the Dutch newspaper De Volkskrant that he had made the decision after considering the unintended consequences that would arise from a ban, including a revival of black-market trade. He also noted that the current system allowed for the government to monitor the quality of “soft” drugs and to limit access to the coffee shops to those 18 and older, something that would be impossible if the trade were again to become clandestine.

“The 1.5 million tourists will not say, ‘Then no more marijuana,’ ” Mr. van der Laan told De Volkskrant, according to a transcript of the interview provided by his office.

“They will swarm all over the city looking for drugs,” he said. “This would lead to more robberies, quarrels about fake drugs and no control of the quality of drugs on the market. Everything we have worked toward would be lost to misery.”