This re-analysis of a previously conducted randomized controlled trial showed that patients who received an incorrect dose of a fibrinolytic agent (alteplase or tenecteplase) for treatment of ST-segment elevation myocardial infarction were more likely to experience adverse clinical outcomes. However, the analysis also showed the same increased risk for patients who received incorrect doses of the placebo versions of the study drugs. Many of the clinical factors that placed patients at risk for adverse outcomes also placed them at risk for dosing errors. This type of confounding is important to keep in mind when attributing adverse outcomes to antecedent errors in care.