OBJECTIVES As the US reimbursement landscape becomes increasingly restrictive, we hypothesized that health technology appraisals (HTAs) published by the National Institute for Clinical Excellence (NICE; UK) would influence drug prescribing and expenditures in the US. The primary objective was to determine whether HTAs have impacted trends in prescription volume (TRx), average retail price (ARP) and out-of-pocket costs (OPC) of 11 drugs covered in recent HTAs. METHODS Six NICE HTAs published since 2007, evaluating a total of 11 non-injectable drugs, were analyzed, of which three freely advocated use of the drugs studied, two encouraged use for restricted populations and one discouraged utilization. TRx, ARP and OPC were collected monthly for the same duration pre- and post-HTA until November 2008. Parameters were collected using SDI's VONA and VOPA databases. Statistical analyses were performed using one-way ANOVA; statistically significant results had p<0.05. RESULTS A NICE appraisal supporting the use of four Alzheimer's drugs (donepezil, galantamine, rivastigmine, memantine) was associated with significant increases in TRx, ARP and a nearly significant increase in OPC (p<0.07). There was a significant decrease in OPC of hepatitis B drug, entecavir, correlated with an HTA supporting its use in addition to a discouraging guidance of its competitor, telbivudine. Guidance restricting the population and duration to receive hyperparathyroidism drug, cinacalcet, was associated with significant increases in TRx, ARP and OPC. An HTA cautiously highlighting the success of opioid-abstinence drug, naltrexone, in counseled patients correlated with significant increases in all three market metrics. CONCLUSIONS NICE HTAs decisions appear to be associated with mixed effects on prescription utilization and expenditures in the US. The influence of NICE decisions on the US market should be monitored as HTAs are expected to play a more significant role in a more judicious reimbursement environment, in which payers increasingly seek evidence to support formulary decisions.