Drug use among older adults has increased sharply over the past decade. The combination of the aging and increasing use of psychoactive drugs, including misuse of prescription psychotropic medications, creates a growing public health problem with rising numbers of older adults at risk for experiencing harm from drug use. This problem is exacerbated by the fact that older adults are more susceptible to the harms of drug use due to age-associated physiological changes, social factors such as increased isolation, increases in comorbidity, and use of medications that may interact with other drugs. There is a lack of reliable estimates of drug use among older adults that may contribute to the perception that they do not engage in use, making them less likely to be screened for use. As such, we believe the prevalence of drug use among older adults is underestimated. More focused surveys assessing drug use aimed at older adults are needed. Additionally, intentional and unintentional underreporting of drug use remains common across populations. Combining surveys with biological testing could detect underreporting and unintentional exposure to drugs, and this combination can also be used to adjust estimates of use. Thus, assessing drug use through surveys plus biological testing will provide important information that informs how both researchers and clinicians screen and address drug use in this population. Our multidisciplinary team has extensive expertise in drug use epidemiology among older adults, survey design, population sampling, and advanced toxicology testing. We will administer a rapid drug survey to query use of ~100 illegal drugs and a variety of prescription psychoactive drugs in 300 adults aged ≥65 in New York City. We will calculate the prevalence of use of a wide variety of drugs and assess the value of adding saliva testing and hair testing to the survey. We will apply a targeted street intercept sampling approach to reach diverse older populations often overlooked by national surveys, including people experiencing homelessness. We can test exposure to >1,000 drugs including over 100 fentanyl analogs. The aims of this project are to: 1) determine if and to what extent saliva and hair testing add to the prevalence of self-reported drug use, 2) delineate risk factors for testing positive for exposure after not reporting use (discordant report) and deduce the extent to which discordant report is from unknown adulterant exposure vs. misreporting, and 3) characterize use of cannabis and other illegal drugs in terms of reasons for use, route(s) of administration, and whether adverse effects (including substance use disorder) have resulted from use. This interdisciplinary research spanning aging research and drug use epidemiology will inform public health responses and improve age-friendly health systems to address the increase in psychoactive drug use and its adverse health effects among older adults. This study will not only inform how resear...