OBJECTIVES: Since 2011 therapeutic tendering of antiretroviral drugs (ARVs) in London has saved over £10 million annually (~5% of London’s annual ARV budget). The objective of this research was to understand how therapeutic tendering practices in London impact the use of ARVs. METHODS: Qualitative in-depth interviews with 10 former London commissioners and senior HIV clinicians. RESULTS: In England, branded ARVs are procured via regional therapeutic tenders, with the lowest-cost product within a therapeutic class being awarded a 2-year price/volume-based contract. To realize price/volume savings, regional prescribing guidelines are published following the tender, recommending the use of the contracted product at the expense of other drugs within the class. Although regional adjudication and clinical consensus are required before implementing any cost-saving plans, price is a crucial factor determining the uptake of ARVs at the regional level. Along with obtaining low prices by creating price competition among branded ARV products, London commissioners have also successfully pushed for the use of generic efavirenz as the first-line therapy for new patients, even though current BHIVA guidelines do not recommend it as the preferred first-line choice. Commissioners mandate that at least 70% of all new patients are prescribed efavirenz in spite of the availability of newer highly effective and better tolerated ARVs. Deviation from the mandate requires documented explanation on an individual patient basis and approval at Multidisciplinary Team meetings. Interviewed clinicians noted that commissioners’ influence over prescription choices in London is substantial, as evidenced by the generated savings and budgetary pressure in the form of reduced average per-patient costs that force clinicians to prescribe therapies that may not always be clinically appropriate. CONCLUSIONS: Regional therapeutic tendering promotes the use of the lowest-cost drugs within a therapeutic class. Consequently, cost is one of the primary drivers of prescription choice of ARVs in London.