Amsterdam and Antwerp are known for their high use of cocaine. But a probe of European waste water shows use of the drug in Switzerland is just as prevalent.
Figures from a new international study suggest about 356 kilograms of cocaine are used every day in Europe. But the stimulant is more popular in central and western Europe than in the east or the north.
Swiss cities are among the places where consumption is highest. In cities like Zurich, Geneva and Bern, an average of 1.5 grams are consumed daily per 1000 people - the same as in cities like Antwerp and Amsterdam.
During techno festivals like Zurich's Street Parade each August, it is thought that people can take up to five or six times this amount.
"Zurich, Geneva and St. Moritz have always ranked highly in cocaine statistics. But it's only a phenomenon in the cities, especially in the club and nightlife scene - not in the whole country," says Tibor Rasovszky, a senior physician at Arud, a centre for addiction medicine in Zurich.
Cocaine use rises during Zurich's annual Street Parade - although this couple looks high enough on love
Waste water analyses conducted in Zurich by the University of Bern show that cocaine consumption in the city almost doubled over a period of three years - from about 11,600 lines of cocaine in 2009 to 21,000 lines in 2011.
It looks like a dramatic rise. But Rasovszky disputes the figures.
"Cocaine use in Switzerland is rising only slightly," Rasovszky says. "In the 90s, we saw an enormous increase but the numbers have been more or less constant for ten years."
The Bern University researchers took their samples from Zurich's waste water each year around the time of the Street Parade. And Rasovszky believes this explains the rise.
"Visitors from all over Europe come to Zurich during the festival," says Rasovszky.
Sifting through waste water
Drug consumption is often determined by the number of people known to seek help for substance abuse.
But the numbers are not always reliable.
"If it is based on self-reporting, then people can exaggerate or understate - or maybe they don't even know what they have been taking," says Christoph Ort of the Swiss federal Institute of Aquatic Science and Technology.
So, researchers are looking for new ways to measure drug use and one way is to analyze waste water samples.
"We're looking for the molecule cocaine as well as the metabolite," Ort explains.
Cocaine molecules show up if the drug is flushed into the system in it unconsumed state, whereas the metabolite is the product after it has been consumed and processed by the body.
And the researchers compare the two values.
Similar studies have been carried out using water from the River Rhine.
Ort was involved in the international study which analyzed waste water from a total of 19 European cities.
Amsterdam showed the highest rates of cocaine use and was followed by Antwerp and London.
Swiss cities were not included in the international probe. But Ort compared these latest numbers to those of a similar study in Switzerland a year ago. In the Swiss study, Zurich, Bern, and Geneva reached the same levels as Amsterdam.
Nordic countries prefer amphetamines
The lowest level of cocaine consumption was found in Stockholm, Oslo and Helsinki.
In the Scandinavian cities, average daily use was estimated at only 0.15 grams per 1000 people.
"There's no definitive explanation for this," says Professor Jørgen Bramness at the Norwegian Centre for Addiction Research at Oslo University, "but the use of narcotics is conservative."
Bramness suggests there are traditional drug-taking habits which vary from country to country.
"Norway has been an amphetamine country for decades," says Bramness. "Cocaine is a newer drug to the Nordic scene."
Injecting drugs - including some amphetamines - is more common in Scandinavia than drugs which are usually taken orally, snorted or smoked.
This could simply be because amphetamines are easier to buy in Scandinavian countries than other drugs like cocaine.
Drugs in Scandinavia are traditionally smuggled in from eastern countries like Russia, says Bramness, while "drugs in southern Europe come from the Americas with a higher influx of cocaine."