OBJECTIVES: To analyze the market impact of the introduction of the COX-2 inhibitors, Celebrex and Vioxx, within the NSAID class and other therapeutic classes that constitute the analgesic market. METHODS: The study design was a retrospective study of paid pharmacy claims for analgesic medications for a continuously insured population of 62,614 members from July 1996 to June 2001. Claims were divided into seven therapeutic categories: hydrocodone, narcotics, non-narcotics, newer NSAIDs (Relafen, Daypro, Arthrotec), older NSAIDs, oxycodone, and COX-2 inhibitors. Data of paid analgesic pharmacy claims were analyzed by overall analgesic market prescription claims, day supply, pain management therapies, per diem cost (ingredient cost per day supply) and market share per therapeutic category. RESULTS: Over the 5-year period, claims increased 29.1% while day supply per claim increased 17.7% for a total growth in day supply of almost 52%. The proportion of the population who used an analgesic also increased from 33.4% in the first year to 37.9% in the fifth year. There was a 15% increase in people receiving at least one analgesic prescription in a year over the 5-year period. Per diem costs for the market increased from $1.74 in the first year to $2.20 in the fifth year. Per member per month costs increased 69.3% from $12.36 in the first year to $20.93 in the fifth year. COX-2 inhibitors market share by day supply increased from zero to 39.6%. The market share of the newer NSAIDs decreased from 20.5% in the year prior to the introduction of the COX-2 inhibitors (year 2) to 5.5% in the fifth year. CONCLUSIONS: Based on day supply, the analgesic market grew almost 52% with COX-2 inhibitors garnering 39.6% within 3 years of market introduction. The COX-2's benefited from both the growth in the market and reduction in market share of the newer NSAID's.