["Addiction, Volume 121, Issue 6, Page 1530-1540, June 2026. ", "\nAbstract\n\nBackground and aims\nCanada's drug toxicity crisis has been largely attributed to a volatile fentanyl‐dominated unregulated drug supply with increasing reports of fentanyl detected in combination with benzodiazepines, stimulants and xylazine. Although rates of opioid‐related harms vary significantly by region, it remains unknown how the composition of the unregulated drug supply differs across Canada. Therefore, we sought to describe trends in Canadian fentanyl‐containing drug seizures nationally and compare trends by province/territory.\n\n\nDesign\nRepeated cross‐sectional analysis between February 2020 and December 2024.\n\n\nSetting and cases\nFentanyl‐containing drug samples seized by law enforcement agencies across Canada were analyzed by Health Canada's Drug Analysis Service, with test results made publicly available.\n\n\nMeasurements\nCounts and crude rates of fentanyl‐containing drug seizures, with the population of each province/territory used to calculate rates per 100 000. We described the number of notable drug classes (e.g. benzodiazepines, stimulants, non‐fentanyl opioids, etc.) and chemical substances identified within each drug seizure and used the Cochrane Armitage Test for Trend to look for significant changes over time. All analyses were conducted overall and stratified by province/territory.\n\n\nFindings\nWe identified 71 996 fentanyl‐containing drug seizures over the study period, with the quarterly number of seizures increasing by 24.4% (from 2640 in 2020 to 3284 in 2024) across Canada. This varied by province/territory, with the highest annual rates of fentanyl‐containing seizures in 2024 reported in British Columbia (60.4 per 100 000) and Alberta (52.3 per 100 000). Among fentanyl types, we observed statistically significant increases (P < 0.001) in the detection of para‐flurofentanyl (0.0% to 46.3%) and methylfentanyl (0.0% to 28.6%). Additionally, there was a notable rise in the annual proportion of seizures in which benzodiazepines (13.4% to 40.2%) or xylazine (1.5% to 18.9%) were detected. Approximately half of all seizures contained fentanyl in combination with at least one other drug class and over 95% contained fentanyl in combination with at least one other chemical substance.\n\n\nConclusions\nAcross Canada from 2020 to 2024, there has been a 24% increase in fentanyl‐containing drug seizures in which multiple substances are detected, most notably benzodiazepines, xylazine and potent fentanyl analogues within a single sample.\n\n"]