Misuse of prescription medications has led to higher mortality and morbidity in the U.S. This study investigates medical and nonmedical use of prescription medications (prescription pain relievers, stimulants, prescription tranquilizers, and sedatives) among adults aged ≥50 years. Data were from the 2015-2017 National Survey of Drug Use and Health. For each prescription medication, medical and nonmedical use were mutually exclusive (prescription pain relievers, stimulants, tranquilizers, and sedatives). Nonmedical use (misuse) was defined as the use of any prescription medications in greater amounts, frequency, or duration than prescribed or the use of medications without a prescription of the individual's own. Descriptive analysis was performed to assess prescription medication use and misuse among adults aged ≥50 years (pooled N=26,322). Correlates of misuse were assessed within multivariable logistic regression analyses at p<0.05. All analyses were conducted in 2019. In the past 12 months, 46.7% (51.7 million) of adults reported using any prescription medication, of which 7.7% (4.0 million) reported misuse. The proportion of past 12-month users reporting misuse was 5.4% for sedatives, 6.4% for prescription pain relievers, 6.5% for prescription tranquilizers, and 8.1% for stimulants. Overall, 16.2% (17.9 million) reported using 2 or more prescription medications within the past 12 months. Multiple prescription medication use was associated with female sex; White race; younger age; and use of nonprescription substances, including alcohol, tobacco, marijuana, and heroin. It is important to monitor medication misuse behaviors among older adults who may be living with several chronic conditions requiring pain management. The strong associations with serious psychological distress underscore the need for increased access to mental health services among this key population.