Glycopyrronium is a once-daily, inhaled long-acting muscarinic antagonist (LAMA) demonstrating similar efficacy to inhaled tiotropium in patients with moderate-to-severe COPD; however, the benefit of LAMAs on COPD symptoms has been variable. COPD is a progressive disease in which many patients develop an acute or sustained deterioration. Data on the prevention of clinically important deteriorations (CID) using LAMAs are limited. A pooled analysis was performed on four Phase III trials (n = 2936) that compared the efficacy of glycopyrronium (n = 1859) with tiotropium (n = 1077). The primary endpoint was significant delay and/or reduction in the occurrence of CID. CID was defined as any of the following: ≥100 mL decrease from baseline in pre-dose forced expiratory volume in 1 second (FEV1), ≥4 point increase in St George's Respiratory Questionnaire score or a moderate-to-severe COPD exacerbation occurring after the first dose of study medication. A sustained CID was a CID occurring on ≥2 consecutive visits 4 weeks apart or for ≥50% of all available subsequent visits. Baseline characteristics for the overall population were similar. Patients had moderate (62%) or severe (38%) COPD. Mean post-bronchodilator FEV1 was approximately 55% predicted, and mean FEV1 reversibility was 16.7 and 18.6% in the glycopyrronium and tiotropium groups, respectively. Both glycopyrronium and tiotropium significantly reduced time to CID and sustained CID versus placebo (p < 0.001). No statistically significant differences were found between the glycopyrronium and tiotropium treatment groups in time to CID or sustained CID. Glycopyrronium is effective in delaying time to clinically important deteriorations, with similar efficacy to tiotropium.