Cocaine use in several Swiss cities is among the highest in Europe, researchers said on Monday.
"The amounts of cocaine ... were in the same range as those European cities with the highest consumption," said Christoph Ort, from the Swiss Federal Institute of Aquatic Science and Technology (Eawag).
The findings were based on research carried out into waste water from 15 million people in 19 European cities and published in the journal Science of the Total Environment.
Bern, Geneva, Lucerne and Zurich are on a par with Antwerp and Amsterdam for use of the class A drug, said scientists from Eawag, who compared the Europe-wide data published in the journal with their own research gathered in Switzerland last year.
Approximate cocaine consumption in Swiss cities is equivalent to 1.5 grammes per day per 1,000 people, according to Eawag's estimates.
Consumption of the lifestyle drug can double and even quadruple at the weekend during events such as the Zurich Street Parade and Music Festival, Eawag said.
In total, some 356 kilogrammes of cocaine is used every day in Europe, according to the research, which amounts to approximately 10 to 15 percent of global production of the drug, according to the United Nations Office on Drugs and Crime.
Barcelona, London, Milan and Paris registered average use of between 0.5 grammes and 1 gramme of the drug, while Scandinavian cities such as Stockholm, Oslo and Helsinki had the lowest level at 0.15 grammes per 1,000 people.
The research also indicated that the drug is used most in central and western Europe rather than eastern and northern Europe.
In addition to tracing drugs in waste water, Eawag investigates levels of pharmaceuticals and household chemicals to reduce pollution.