The stability of drugs proscribed under the Victorian Road Safety Act 1986 (MDMA, MA and THC) was determined in authentic drug-positive oral fluid following short-term storage at room temperature, 4°C, fluctuating temperatures and long-term storage at -20 °C. Following pH adjustment with ammonium carbonate solution, drugs were extracted using chloroform:isopropanol (9:1) and analysed by LC-MS/MS operating in multiple reaction monitoring mode. The results were analysed using Wilcoxon matched-pairs signed ranks and interpreted in the context of AS4760:2006 cut-offs. For MA and MDMA only minor changes occurred following all storage conditions, but THC concentrations were reduced by 70-87% (n=10) following storage at fluctuating temperatures (room temperature to 60°C) for 2 weeks. Of the 10 samples that were positive for THC prior to storage, only one remained positive after 2 weeks. This has significant implications for the interpretation of THC concentrations in cases where the possibility exists that samples were stored at higher temperatures.