Marijuana became legal in Canada in October 2018. Like many states in the U.S., government officials are struggling with how to manage, measure and understand both legal and illegal use of cannabis. This is where the study of human excrement comes in.

Sewage in several municipalities will be studied to gain knowledge of cannabis use. The organization coordinating this activity is Statistics Canada.

The governmental statistical agency knew that it would need to develop a variety of collection strategies and instruments, and look at the country’s infrastructure to obtain the information necessary to quantify the economic and social impact of legal adult use of cannabis.

Statistics Canada will use a process referred to as wastewater-based epidemiology (WBE) to estimate cannabis use by the general public in several Canadian municipalities. The process can identify trends with other drugs, but cannabis is the most common and is of current interest.

Using WBE to estimate drug use is not novel and has been adopted by many countries for over a decade. The methodology is not complex in theory.

In a municipality, daily samples are acquired over time. The sampling may occur from several wastewater treatment plants in a municipality. Samples are collected and kept refrigerated. The flow of sewage is documented, and calculations are made to estimate overall use of a drug per person. Using WBE to estimate cannabis use has some advantages:

• low collection costs
• no burden on household or business respondents
• no infringement of personal privacy or confidentiality
• real-time reporting
• low or no response bias
• ability to develop geographically granular estimates
• ability to detect short-term trends in response to policies and changing conditions
• capacity for retrospective analysis for other drugs and metabolites, using stored samples

Early results from five cities in the months of March and August leading up to legalization showed Halifax to have had the highest rate of consumption, followed by Montreal, Toronto, Edmonton and Vancouver having the lowest usage of the five.

The system is not perfect, as acknowledged by Anthony Peluso, a researcher working on the project and an assistant director at Statistics Canada. He said the goal was to track consumption data consistently.

"There may be some flaws in it, but I think if the flaws are consistent over time, then the trend will emerge," he said.

Not all epidemiologists are enthusiastic. M-J Milloy, an epidemiologist at the British Columbia Centre on Substance Use and a professor of cannabis science told The Globe and Mail newspaper that, "The problem is, the amount of THC that is detected in waste water is dependent upon how strong the cannabis [is], … The temperature of the water, the limpidity of the water, what kind of chemicals the city has put in their drinking water — all sorts of factors will affect how much THC is finally detected."

He further stated, "In my view, these are fundamental flaws, and it renders any of their estimates unusable. Perhaps there will be developments in the future that will change my mind, but I don’t think there’s a lot of valuable evidence here at this point."

With limited resources and concerns about privacy, the approach of learning from anonymous poop about pot certainly seems promising. Poop and pot studies may be coming to your town eventually.