AIMS: We quantified concomitant medicine use and occurrence of potential drug-drug interactions in people living with HIV in Australia who are treated with antiretroviral therapy (ART). METHODS: In this cohort study using dispensing claims of a 10% random sample of Australians, we identified 2230 people dispensed ART between January 2018 and December 2019 (mean age 49.0 years, standard deviation 12.0 years, 88% male). We examined concomitant medicine use by identifying nontopical medicines dispensed within 90-days of any antiretroviral medicine dispensing during a 12-month follow-up period. For every antiretroviral and nonantiretroviral pair, we identified and classified possible drug-drug interactions using the University of Liverpool HIV drug interactions database. RESULTS: A total of 1728 (78%) people were dispensed at least 1 and 633 (28%) 5 or more unique medicines in addition to ART in a 12-month period; systemic anti-infectives and medicines acting on the nervous system were the most common (68% and 56%, respectively). Among comedicated people, 1637 (95%) had at least 1 medicine combination classified as weak interactions, 558 (32%) interactions requiring close monitoring/dose adjustment and 94 (5%) that should not be coadministered. Contraindication or interactions requiring close monitoring/dose adjustment were more common among people receiving protease inhibitors (50-73% across different antiretrovirals), non-nucleoside reverse transcriptase inhibitors (35-64%), people using single-tablet combinations containing elvitegravir (30-46%) and those using tenofovir disoproxil (26-30%). CONCLUSION: Concomitant medicine use is widespread among people living with HIV in Australia. Despite a relatively low prevalence of contraindicated medicines, almost a third received medicines that require close monitoring or dose adjustment.