OBJECTIVE: To assess the economic impact to the US payer of recombinant human growth hormone (rHGH) utilization in an adult population. METHODS: rHGH may be administered to adults via vial/syringe or pen injection systems provided by six manufacturers. Variation in annual drug cost is largely a function of dosing efficiency and price per milligram (mg). A budgetary impact model was developed to calculate drug costs based on product waste and cost. Waste was calculated as the difference between prescribed dose, based on patient weight, and actual delivered dose, based on dosing increments and maximum deliverable dose for pens and a fixed percent waste as derived from the literature for vials. Annual drug costs were calculated based upon total mg delivered, using a daily dose of 0.016 mg/kg and wholesale acquisition cost. Total annual drug costs, assuming equal use of vials and pens from each manufacturer, were compared for two scenarios: 1) A mix based on national market share and 2) restricting use to the product with lowest waste. RESULTS: Based on the literature, waste for each vial product was 23%, including injection error (15%) and syringe/needle dead space (8%). Among individual pens, product waste was highest for Humatrope 24mg (14.3%) and lowest for Norditropin NordiFlex 5mg (1.0%). Equal use of vials and pens from each manufacturer resulted in the following product waste: Tev-Tropin 23% (vial only), Nutropin 18.2%, Humatrope 12.2%, Genotropin 5.5%, Saizen 3.8%, and Norditropin 3.0%. Restricting use to the product with least waste (Norditropin) resulted in a 10.5% reduction in annual patient cost from $24,764 to $22,161 compared to a national share mix. CONCLUSION: Pen delivery systems result in less waste than vial and syringe. Considering all approved delivery systems, Norditropin resulted in the least product waste and lower annual patient cost.