OBJECTIVE: Approximately eight million women and two million men in the U.S. suffer from osteoporosis, a disease that causes over 1.5 million fractures each year. The cost to Medicaid for anti-osteoporosis medications topped $85 million in the first quarter of 2004. The objective of this study is to analyze price, cost, utilization, and market shares of oral anti-osteoporosis medications in U.S. Medicaid programs, with the specific purpose of assessing interbrand competition in a tightly oligopolistic market. METHODS: There are five oral medications for osteoporosis, including Didrone (etidronate), Skelid (tiludronate), Actonel (risedronate), Fosamax (alendronate), and Evista (raloxifene). Data from the First DataBank were used to calculate the monthly Average Wholesale Price (AWP) per daily dose for each drug over the period 1990-2004. Data from the National Medicaid Pharmacy claims were used to calculate quarterly drug prescriptions, market shares, and reimbursements over essentially the same time period. RESULTS: The three most frequently prescribed drugs are alendronate (utilization reached 600,000 scripts in the 1st quarter 2004); risedronate whose use increased from 90 scripts in the 2nd quarter 1999 to 400,000 in the 1st quarter 2004; and raloxifene with utilization of 190,000 scripts in the 1st quarter 2004. Each of these drugs has an AWP per daily dose in the $2.00-to-$4.00 range. Interestingly, the Medicaid cost per prescription for risedronate decreased from $300 in 1999 to $80 in 2004. Though not widely prescribed, the AWP for tiludronate is much higher than for its competitors at $15.00 per daily dose. CONCLUSIONS: There is no indication that market shares or prices of branded medications are responding to new entry in the anti-osteoporosis drug market. Movement in prices and utilization are driven much more by dosage and compliance issues.