INTRODUCTION: This study examines illicit opioid samples submitted to a drug checking service in British Columbia, Canada. By employing a method capable of identifying and quantifying compounds at low concentrations, the analysis focused on identifying trends in notable compounds such as fentanyl, its analogues, and benzodiazepines. The findings aim to address gaps in supply monitoring and inform public health and drug policies. METHODS: Opioid samples were collected and analyzed over three years using fentanyl and benzodiazepine test strips, Fourier-transform infrared (FTIR) spectroscopy and Paper-Spray Mass Spectrometry (PS-MS). PS-MS was employed to conduct trace-level analysis, provide targeted composition results, and quantify notable ingredients within the samples. The concentrations of fentanyl and benzodiazepines, among other components, were examined. RESULTS: The dataset includes 8122 opioid samples analyzed from January 2021 to December 2023. Analysis revealed that heroin was replaced by fentanyl and its analogues in the opioid supply, as heroin was detected in only 4 % of opioid samples while fentanyl and analogues were detected in 88 %. Fluorofentanyl was found in 70 % of opioid samples, occasionally in combination with fentanyl. Benzodiazepines and their analogues were detected in 49 % of opioid samples, with a notable shift from etizolam to bromazolam. The median fentanyl concentration was 10.6 % (weight/weight), ranging from less than 0.1 % to over 80 %. The median bromazolam concentration was 3.2 %, with a range of less than 0.1 % to over 25 %. CONCLUSION: The study highlights the volatility in the supply and mentions the necessity for a safer opioid supply and robust drug checking methodologies to address the challenges posed by the heterogenous market.