A 64-year-old woman with obesity [body mass index (BMI) 34.2 kg/m²], type 2 diabetes mellitus (T2DM), hypertension, hyperlipidaemia, and previous acute coronary syndrome (ACS) treated with percutaneous coronary intervention (PCI) presented to the emergency department in January 2019 with symptoms consistent with a transient ischaemic attack (TIA) while receiving dual antiplatelet therapy (DAPT) with aspirin and clopidogrel. Her cardiovascular history included coronary artery bypass grafting (CABG) following a cerebellar stroke in 2016 and repeat PCI with drug-eluting stent implantation in 2018. She reported good adherence to treatment and denied a history of smoking, alcohol use, renal failure, or proton-pump inhibitor use. Routine laboratory investigations were unremarkable except for obesity, suboptimally controlled diabetes [glycated haemoglobin (HbA1c) 7.7%], and mild anaemia (haemoglobin 11.1 g/dL). Following the recurrent TIA, the neurology team requested CYP2C19 genotyping, which identified a CYP2C191/2 genotype, consistent with an intermediate metaboliser phenotype. Based on these findings, clopidogrel was discontinued, and ticagrelor (90 mg twice daily) was initiated while aspirin therapy was continued. During three years of follow-up, the patient remained clinically stable without recurrent TIA, stroke, myocardial infarction, stent thrombosis, or other major adverse cardiovascular events (MACE).