Cannabis crashes 90% as cocaine surges in Chilean sewage study

A groundbreaking two-year study from Chile's Biobío Region used wastewater-based epidemiology (WBE) — a technique that analyzes sewage for drug metabolites — to track real-world community drug use patterns between September 2022 and August 2024. Researchers collected 3,198 samples from 33 wastewater treatment plants, testing for the cannabis metabolite 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH), cocaine byproducts, and ketamine. This represents the first large-scale, multi-year regional WBE program ever conducted in Chile, offering an unprecedented ground-level view of how drug consumption is shifting across South-Central Latin America.

The results for cannabis were striking: community cannabis consumption fell by over 90% during the study period, making it one of the sharpest documented declines in cannabinoid use ever captured by wastewater surveillance. Simultaneously, cocaine use surged by more than 1,000%, and ketamine rose from completely undetectable levels to measurable concentrations across multiple locations. A strong inverse correlation was observed between cannabis use and both cocaine and ketamine, suggesting a dramatic substitution shift in the regional drug landscape — away from cannabinoids and toward stimulants and dissociatives.

For cannabis researchers and public health officials, this study underscores both the value and the limitations of traditional drug surveys. Wastewater-based epidemiology can detect rapid, real-world shifts in consumption that might take years to surface in self-reported surveys or seizure data. The findings suggest that urban areas remain the primary hotspots for drug use of all kinds, and that policy responses in Latin America must adapt quickly to a fast-moving drug environment. The methodology itself — SPE/LC-MS/MS analysis — offers a scalable, cost-effective blueprint for other regions seeking real-time public health monitoring.