Cannabis consumption rates can be measured in various ways, with self-reporting via surveys being a common method. However, self-reporting is not always reliable due to prohibition policies. It shouldn’t be surprising to know that when people are asked if they consume a substance that could land them in jail, they are not always forthcoming about their use.

Even in jurisdictions where cannabis is legal, some patients and consumers will not admit to use due to ongoing stigma. Stigma is thankfully reducing in such jurisdictions, but it is not entirely gone. Hopefully as time goes by, the trend of reduced stigma will continue.

Another method for measuring cannabis use, and the use of other substances for that matter, is analyzing wastewater. The European Union Drugs Agency (EUDA) recently released a multi-city study that examined substances found in wastewater. The study included rates of cannabis metabolites in wastewater for several European cities.

“The analysis of municipal wastewater for drugs and their metabolic products to estimate community consumption is a developing field, involving scientists working in different research areas, including analytical chemistry, physiology, biochemistry, sewage engineering, spatial epidemiology and statistics, and conventional drug epidemiology.” EUDA stated about its study.

“The project analysed wastewater in around 115 European cities and towns (referred to as ‘cities’) to explore the drug-taking habits of those who live in them. The results provide a valuable snapshot of the drug flow through the cities involved, revealing marked geographical variations.” EUDA also wrote.

The European Union Drugs Agency estimates that 24 million European adults consumed cannabis at least once during the last year, which works out to about 8.4% of the continent’s adult population. Part of the EUDA study compared cannabis usage rates in Europe to Canada and the United States, with cannabis usage rates being greater in North America.

Below is a map published by EUDA, displaying “relative geographical distribution of cannabis metabolite as detected in European cities” for the 2025 calendar year:

“From 2024 to 2025, the overall loads of cannabis metabolites detected in wastewater in European cities remained stable. The highest loads of the cannabis metabolite THC-COOH were found in cities in the Netherlands, Germany and Slovenia.” EUDA wrote about the study’s results.

Below is a map displaying “changes in the mean weekly cannabis metabolites from wastewater analyses in selected European cities between 2024 and 2025”:

The full study, including table data, can be viewed at the European Union Drugs Agency’s website.