ObjectiveTo evaluate the adherence to treatment, resource use, and costs in subjects initiating treatment with brand-name versus generic clopidogrel for acute coronary syndrome (ACS) and peripheral arterial disease (PAD). Patients and methodsObservational, retrospective study based on the medical records of patients aged ≥18 years who initiated treatment with clopidogrel (brand-name vs. generic) between 4 April 2015 and 31 March 2017. Four study groups were compared, and the follow-up was one year. The main measurements were: comorbidity, treatment adherence, medication possession ratio (MPR), resource use, and costs. The results were analysed using multivariate analysis. The level of statistical significance was P<.05. ResultsFour groups were compared: a) ACS: brand-name clopidogrel (N=1,067) vs. generic (N=3,504), and b) PAD: brand-name clopidogrel (N=425) vs. generic (N=994). In the ACS comparison (mean age: 69.7 years, 61.4% male), adherence (65.3% vs. 61.0%, P<.001), adjusted hazard ratio 0.85 and MPR (89.8% vs. 86.7%, P=.045) were more superior with brand-name clopidogrel than with the generic and with a lower mean cost per unit (€2,890 vs. €3,865, P=.001). In the PAD comparison, similar results were observed: persistence (64.7% vs. 58.9%, P=.039); adjusted hazard-ratio 0.86 and MPR (88.6% vs. 81.7%; P=.013) were more superior with brand-name clopidogrel than for the generic, with a lower mean cost per unit (€2,880 vs. €3,532, P=.044). ConclusionsThere was better treatment adherence in patients initiating treatment with brand-name compared with generic clopidogrel for ACS and PAD, resulting in lower health costs for the Spanish National Health System.