Rates of overdose deaths involving synthetic opioids remain high, increasingly involve stimulants combined with opioids, and are increasing rapidly in racially and ethnically minoritized communities, yet little is known about access to harm reduction and treatment services in these groups. To characterize access and barriers to harm reduction and treatment in a racially and ethnically diverse population of people who use drugs. A cross-sectional telephone survey of people recruited from 39 treatment, harm reduction, and social service organizations in Milwaukee County, Wisconsin; Flint and Detroit, Michigan; and statewide in New Jersey was conducted from January 30 to July 28, 2023. Adults who used cocaine, methamphetamine, or opioids in the past 30 days called a study hotline and completed an interview in English or Spanish. Overdose experience, drug types used (opioids only, stimulants only, and polysubstance), and social risk factors (eg, financial instability and criminal legal involvement). Recent use of any harm reduction services, fentanyl test strips, naloxone possession, treatment, and self-reported barriers to services. Of the total sample of 1240 adults, 486 (39.2%) were Black non-Hispanic, 183 (14.8%) were Hispanic, and 464 (37.4%) were White non-Hispanic. In the past 30 days, 826 individuals (66.6%) were polysubstance users, 135 (10.9%) used only opioids, and 279 (22.5%) used only stimulants. A total of 349 respondents (28.1%) experienced a prior-year overdose. Compared with those without a prior-year overdose, people with overdose were more likely to possess naloxone (80.7% vs 68.2%; P < .001), possess fentanyl test strips (36.8% vs 23.5%; P < .001), and use harm reduction services (63.4% vs 53.0%; P = .003), while differences in treatment use were nonsignificant (52.0% vs 46.6%; P = .24). Among stimulant-only users, 51.4% possessed naloxone compared with 77.3% of opioid-only users (P < .001) and 77.6% of polysubstance users (P < .001), with similar disparities in fentanyl test strip possession. In this cross-sectional study of people who used drugs in the past 30 days, findings highlighted low use of harm reduction and treatment services among people who use stimulants. Additional communication regarding their importance may help increase the use of the services amidst a rapidly changing drug supply.