This postmarketing observational study assessed the safety and efficacy of short-term treatment with prasugrel in patients with ACS in real-world clinical practice settings in Japan. We consider that this study provides relevant information in terms of the efficacy and safety of prasugrel as we included patients with severe cardiac disease (Killip IV) (6.7% of patients), history of ischemic stroke (5.1%), and severe renal impairment (on dialysis) (2.0%), as well as those concomitantly taking drugs that increase the tendency of bleeding AEs, such as warfarin/DOACs (2.6%) or NSAIDs (1.5%). Patients having these baseline demographics and/or taking these concomitant drugs (approximately one-sixth of the patients) were excluded from clinical studies in Japan, such as PRASFIT-ACS .