MOTIVATION. An increasing number of U.S. states/localities are loosening or considering changing their policies about psychedelic substances such as psilocybin. To project the health and economic consequences of policy changes, we need better information about use patterns, supply sources, and expenditures. Because detailed information about psilocybin consumption/supply is not collected as part of nationally representative surveys in the U.S., we fill this gap. DATA. Our main survey was fielded as part of NORC’s AmeriSpeak panel which is representative of the entire U.S. adult population because it leverages the NORC National Frame, an area probability sample used for landmark studies like the General Social Survey (N=3,500). We supplement this with a national convenience sample of approximately 2,000 people who used psilocybin in the past year (>25% reported using in the past month). Both surveys include detailed questions about psilocybin prevalence, frequency, product type, supply source, expenditures, intensions for use, and whether the most recent experience was supervised. RESULTS. Forthcoming. Data collection started in 11/2023 and will be finished by 1/2024. Analyses will be completed by 4/2024. In addition to presenting descriptive statistics about psilocybin use and supply, we will generate the first national estimates of the U.S. psilocybin market and compare it with what is known about markets for cannabis and other substances. DISCUSSION. We will offer thoughts about what these results mean for conducting policy analyses and ideas about how to improve data collection on psilocybin/psychedelics.