Investigators conducted a cross-sectional study involving a random sample of Medicare beneficiaries with Part D prescription drug coverage and known diagnosis of HIV.  For each year from 2013 to 2021, two authors independently reviewed the list of prescribed ARVs and categorized them as either “non-recommended” or “preferred”: “non-recommended” agents were generally those with higher toxicity profile and availability of more effective alternatives, in accordance with DHHS Guidelines during that period.  In this sample, 1,052 beneficiaries with HIV contributing 2,901 person-years filled at least one non-recommended ARV prescription, and 28,019 contributing 135,791 person-years filled only preferred ARV prescriptions.  Beneficiaries taking non-recommended ARVs were more likely to reside in the South (50.5% vs. 45.6%) and less likely to live in the West (13.4% vs. 18.4%).  Investigators noted no meaningful differences by age, sex, race and ethnicity, Medicaid dual eligibility, or Part D Low-Income Subsidy eligibility.  The five most commonly prescribed non-recommended agents were didanosine (797 person-years, 27.5%), nelfinavir (733 person-years, 25.3%), stavudine (644 person-years, 22.2%), saquinavir (445 person-years, 15.3%), and co-formulated abacavir/lamivudine/zidovudine (302 person-years, 10.4%).  The overall proportion of beneficiaries who received at least one non-recommended ARV decreased from 5.1% to 0.1% over the review period.