Introduction The ORBITA trial of PCI versus a placebo procedure for patients with stable angina was conducted across 6 sites in the United Kingdom via home monitoring and telephone consultations. Patients underwent detailed assessment of medication adherence which allowed us to measure the efficacy of the implementation of the optimisation protocol and interpretation of the main trial endpoints. Methods Prescribing data were collected throughout the trial. Self-reported adherence was assessed, and urine samples collected at pre-randomisation and at follow-up for direct assessment of adherence using HPLC MS/MS. Results Self-reported adherence was >96% for all drugs in both treatment groups at both stages. The percentage of samples in which drug was detected at pre-randomisation and at follow-up in the PCI vs. OMT groups respectively was: clopidogrel, 96% vs. 90% and 98% vs. 94%; atorvastatin, 95% vs. 92% and 92% vs. 91%; perindopril, 95% vs. 97% and 85% vs. 100%; bisoprolol, 98% vs. 99% and 96% vs. 97%; amlodipine, 99% vs. 99% and 94% vs. 96%; nicorandil, 98% vs. 96% and 94% vs. 92%; ivabradine, 100% vs. 100% and 100% vs. 100%; and ranolazine, 100% vs. 100% and 100% vs. 100%. Conclusions Adherence levels were high throughout the study when quantified by self-reporting methods and similarly high proportions of drug were detected by urinary assay. The results indicate successful implementation of the optimisation protocol delivered by telephone, an approach that could serve as a model for treatment of chronic conditions, particularly as consultations are increasingly conducted online.