PROBLEM TO BE SOLVED: To provide a novel crystal polymorphism of prasugrel hydrobromide useful, for example, in medicaments that inhibit aggregation of platelets.SOLUTION: The present invention provides specific crystalline forms of prasugrel hydrobromide.【課題】例えば血小板の凝集を抑制する薬剤に有用であるプラスグレル臭化水素酸塩の新規結晶多形の提供。【解決手段】特定の結晶性形態のプラスグレル臭化水素酸塩。【選択図】図6