BackgroundCancer drugs are high risk drugs and medication errors in their prescribing, preparation and administration have serious consequences, including death. The importance of a multidisciplinary approach and the benefits of pharmacists’ contribution to cancer treatment to minimise risk have been established. However, the impact of services provided by pharmacists to cancer patient care is poorly studied. This study explored the clinical interventions made by pharmacists in dispensing of chemotherapy doses, and evaluated pharmacists’ contribution to patient care.MethodsPharmacists at the Chemotherapy Preparation Unit at a tertiary cancer centre in London were shadowed by two research pharmacists during the clinical screening of chemotherapy prescriptions and release of prepared drugs. An expert panel of pharmacy staff rated the clinical significance of the recorded interventions.ResultsTwenty-one pharmacists’ interventions were recorded during the screening or releasing of 130 prescriptions or drugs. “Drug and therapy” (38%), “clerical” (22%) and “dose, frequency and duration” (19%) related problems most often required an intervention, identifying areas in chemotherapy prescribing that need improvement. The proposed recommendations were implemented in 86% of the cases. Many recorded interventions (48%) were ranked to have had a “very significant” influence on patient care.ConclusionClinical interventions made by pharmacists had a significant impact on patient care. The integration of pharmacists’ technical and clinical roles into dispensing of chemotherapy doses is required for providing high-quality cancer services.