OBJECTIVES: ARBs were introduced into the UK antihypertensive drug market at a premium price and during a time of evolving evidence and changes to existing hypertension treatment guidelines. The study aimed to determine the UK antihypertensive drug budget impact since the first ARB market launch December 1994 and what proportion of the increase was directly attributable to ARBs. METHODS: Prescriptions for oral hypertension treatment were identified from 1995 through approximately July 2004 from the Health Improvement Network (THIN) database, an electronic medical record dataset of patients seen by general practitioners in the UK. Drug prices were based on the Chemist&Druggist January 2005 pricelist to estimate real growth in expenditures. Expenditure trends were disaggregated by: (1) treatment prevalence, defined as the number of patients receiving a prescription for an antihypertensive drug; (2) antihypertensive prescriptions per patient treated; and (3) average drug expenditures per antihypertensive prescription. RESULTS: Expenditures for drugs approved for hypertension treatment were estimated at 465,862,416GBP in 1995 and 1,458,268,104GBP in 2004 (2005 GBP values), reflecting a 213% real rate of increase. Use of ARBs accounted for only 5.8 to 9.3 aggregate percentage points of the average drug expenditures. ARB prescription frequency increased from 0.04% in 1995 to 6.57% in 2004. Treatment prevalence rose from 11.30% in 1995 to 16.90% in 2004, while the average annual number of antihypertensive drug prescriptions per patient increased from 9.32% to 13.46%. The average antihypertensive drug expenditures per antihypertensive drug prescription increased over time reflecting a product shift towards more expensive therapies. CONLUSIONS: ARBs accounted for less than 10% of the 213% increase in expenditures on antihypertensive drugs following the introduction of ARBs in the UK. A substantial portion of the indirect impact reflected increases in treatment prevalence and increases in the number of prescriptions per patient, including the use of combination therapies.