Abstract Aims The combination of cagrilintide and semaglutide (CagriSema) is being developed for the treatment of obesity and type 2 diabetes. The objective of this thorough QT study was to confirm that cagrilintide does not result in a clinically relevant prolongation in cardiac repolarization compared with placebo. Materials and Methods This was a double‐blind study (NCT05804162) in which healthy participants were randomized to cagrilintide, administered as a once‐weekly subcutaneous injection dose escalated to 4.5 mg, or a placebo. The primary end point was the time‐matched change from baseline in Fridericia heart rate–corrected QT interval (QTcF) at 12‐, 24‐, 48‐ and 72 h after the last cagrilintide 4.5‐mg dose. To conclude that cagrilintide does not induce a clinically relevant prolongation, the upper limit of the two‐sided 90% confidence interval (CI) for the treatment difference at each of the four time points must fall below 10 ms. To establish QT assay sensitivity, participants in the placebo arms received a single 400‐mg oral moxifloxacin dose as a positive control and moxifloxacin placebo in a nested cross‐over fashion. Results A total of 105 participants received cagrilintide ( n = 53) or placebo ( n = 52). No clinically relevant QTcF prolongation occurred after the last cagrilintide 4.5‐mg dose; the upper limits of the two‐sided 90% CIs of the placebo‐adjusted QTcF changes from baseline were below 10 ms at all time points. QT assay sensitivity was demonstrated with moxifloxacin as a positive control. Conclusions Cagrilintide did not result in clinically relevant QTcF prolongation, indicating no increased risk of ventricular tachyarrhythmias.