Generic drugs are available in the United States and Japan. In the US between 40% and 50% of all prescriptions are generic products. Although the cost advantage of generic drugs is recognized in Japan, physicians are still concerned about the potential for a difference in outcomes from generic vs trade name products. OBJECTIVE: To investigate whether the outcomes in patients taking generic vs. trade name Ranitidine differ in the United States and, based on the results of the study in the US, to assess the difference of treatment costs in generic vs. trade Ranitidine in Japan. METHODS: In the US, Medstat MarketScan (commercial claims) 2000-2001 data was used. Patients 18 and older with at least one prescription for oral Ranitidine were identified. The first Ranitidine prescription fill was the index date. Incidence of GI perforations ulcers or bleeds (PUB) or Other GI events (OGI, e.g. gastritis), and costs were determined for patients with generic or trade name therapy. In Japan, a decision analytic model was introduced to evaluate the costs assuming the same outcomes as in the US. RESULTS: In the US 97,387 generic and 5,117 trade patients were identified. Drug costs ($2538 vs. $4070) and total costs ($9647 vs. $12,501) were lower for generic vs. trade patients. There was no difference in mpr (medication possession ratio) or the incidence of PUB (1.9%). Other GI events were higher (19.7%, 17.7%) for generic Ranitidine. The higher proportion in OGI reduced the advantage of a lower cost generic drug by 10.7% ($51 to $46), estimating the average treatment costs per patient of gastritis/duodenitis for four-week follow-up in Japan. CONCLUSIONS: US Patients on generic ranitidine had lower costs, a similar incidence of PUB and somewhat higher OGI incidence. Also, the higher incidence in OGI reduced the value of generic Ranitidine therapy in Japan.