Surveys of drug use form an important basis for the development of effective drug policies, and also for measuring the effectiveness of existing policies. For the first time in history, scientists have now made direct comparisons of illicit drug use in 19 European cities by a cooperative analysis of raw sewage samples. The data show distinct temporal and spatial patterns in drug use across Europe. Cocaine use was higher in Western and Central Europe and lower in Northern and Eastern Europe. High per capita ecstasy loads were measured in Dutch cities, as well as in Antwerp and London. In general, cocaine and ecstasy loads were significantly elevated during the weekend compared to weekdays. Per capita loads of methamphetamine were highest in Helsinki, Turku, Oslo and Budweis, while per capita loads of cannabis were similar throughout Europe.