Background Antiretroviral (ARV) medications to treat human immunodeficiency virus (HIV) are a major contributor to Medicaid prescription drug spending. Despite having been used for over 3 decades, the first generic ARVs only recently became available, and many newer versions continue to be sold at high prices despite within-class competition. We estimated Medicaid spending on ARVs from 2007 through 2019. Methods Using public Medicaid State Drug Utilization data, we identified trends in ARV spending and use from 2007 through 2019. We estimated net spending and average prices (spending per 30-day supply), accounting for statutory Medicaid rebates, including a 15%–23% base rebate plus additional rebates if a drug's price increased faster than inflation. Results Among 48 ARVs, estimated net Medicaid spending from 2007 through 2019 was $25 billion for 17 million 30-day supplies. Annual use increased 118%, from 0.7 million 30-day supplies in 2007 to 1.6 million in 2019. During this time, estimated annual net spending increased 178%, from $1.1 billion to $3.0 billion, and average net prices increased 28%, from $1432 to $1830 per 30-day supply. Conclusions Annual Medicaid net spending on ARVs nearly tripled from 2007 to 2019, due to a combination of expanded use and rising prices. Medicaid did not extract expected benefits from its mandatory inflationary rebates because they were offset by use of newer, more expensive ARVs. To better control spending related to products with incremental innovation, the US government should be authorized to assure that launch prices for new drugs are aligned with the added benefit they offer over existing therapies. [ABSTRACT FROM AUTHOR]