Estimating the Daily Milligrams of Morphine Equivalent of Illicit Fentanyl Use in Los Angeles: Clinical and Epidemiological Implications

IntroductionThe market shift from heroin to illicitly-manufactured-fentanyl in North America led to surging rates of opioid overdose and mortality. However, limited detailed information exists about the dose of fentanyl regularly consumed by individuals with opioid use disorder. We examined purity of fentanyl samples and estimate the typical daily oral milligrams of morphine equivalent (MME) consumed. MethodsLeveraging community-based drug checking data from Los Angeles, we ascertained the purity of 384 samples of fentanyl collected between September 2023 and July 2025 using liquid chromatography mass spectrometry. We assessed typical consumption quantity and routes of administration among 31 respondents who reported regularly using fentanyl. We drew bioavailability estimates and approximate MME conversion factors from literature. To estimate daily MME consumed, and incorporate uncertainty from all parameters, we used a bootstrapping model with 10,000 draws. ResultsAmong participants, the median daily consumption of fentanyl was 1.0 grams (1000 milligrams). Illicit fentanyl products had a median fentanyl purity of 9.4%., and the median estimated bioavailability based on routes of administration was 72.3%. Using a median IV fentanyl to PO morphine conversion factor of 1:182, the median estimated daily consumption in our sample was 10,933 MME (IQR 25,272 MME). ConclusionsWe estimate that individuals consuming illicit fentanyl in Los Angeles use quantities of opioids that are several orders of magnitude higher than clinical guidelines or typical methadone doses. This undoubtedly contributes to high overdose mortality rates and reflects a high tolerance among individuals with OUD. It also likely undermines the success of medications for OUD at conventional doses.