Abstract Background Cangrelor is an intravenous P2Y12 inhibitor which, according to the European guidelines, may be considered for administration in acute coronary syndrome during percutaneous coronary intervention (PCI). Little is known regarding benefits and risks of such administration in hemodynamically unstable patients. Purpose To investigate the effects of cangrelor versus no cangrelor during PCI regarding major adverse cardiac events (MACE), in-hospital bleeding, and all-cause mortality in patients with cardiogenic shock and/or cardiac arrest. Methods The study population was extracted from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR) and included patients with cardiogenic shock or cardiac arrest undergoing PCI during the years 2016-2022. Propensity score matching (PSM) was used to create comparable groups. After matching, all variables used for calculating propensity score were balanced (standardized mean difference<0.1). Outcomes were MACE within 30 days, in-hospital bleeding, and all-cause mortality within 30 days. Risk ratios (RR) with 95% confidence intervals (CI) were calculated. When RR deviated from the null, the risk difference (RD) was determined. Results In all, 2,100 (66%) out of 3,206 patients with cardiogenic shock and/or cardiac arrest were included in the PSM analyses (median age: 69 years; 76% male; 78% ST-elevation myocardial infarction (STEMI)). Comparing cangrelor versus no cangrelor in this matched set of patients, the RR was 0.93 (95% CI: 0.84; 1.04) for MACE; 1.51 (1.02; 2.25) for in-hospital bleeding, with an RD of 1.9 percentage points (0.10; 3.7); and 0.93 (0.82; 1.04) for all-cause mortality (Table). In the PSM analysis regarding patients with cardiogenic shock, 1,098 (60%) out of 1,815 patients were included (median age: 71 years; 68% male; 82% STEMI). For these patients, RR was 0.85 (95% CI: 0.74; 0.97) for MACE, with an RD of -7.5 percentage points (-1.6; -13); 1.31 (0.82; 2.09) for in-hospital bleeding; and 0.83 (0.72; 0.95) for all-cause mortality, with an RD of -8.0 percentage points (-2.2; -14). In the PSM analysis regarding patients with cardiac arrest, 1,388 (76%) out of 1,827 patients were included (median age: 67 years; 81% male; 75% STEMI). RR was 0.98 (95% CI: 0.86; 1.12) for MACE; 1.53 (0.95; 2.49) for in-hospital bleeding; and 0.98 (0.86; 1.13) for all-cause mortality. Conclusion For patients with cardiogenic shock, but not for patients with cardiac arrest, administration of cangrelor versus no cangrelor during PCI was associated with a reduction in both MACE and all-cause mortality, with numbers needed to treat of 14 and 13, respectively. Overall, for patients with cardiogenic shock or cardiac arrest, administration of cangrelor versus no cangrelor during PCI was associated with an increased risk of in-hospital bleeding with a number needed to harm of 53.