AbstractObjectives The objective of this systematic review was to synthesize the available qualitative evidence on the knowledge, attitudes and beliefs of adult patients, healthcare professionals and carers about oral dosage form modification. Design A systematic review and synthesis of qualitative studies was undertaken, utilising the thematic synthesis approach. Data sources The following databases were searched from inception to September 2015: PubMed, Medline (EBSCO), EMBASE, CINAHL, PsycINFO, Web of Science, ProQuest Databases, Scopus, Turning Research Into Practice (TRIP), Cochrane Central Register of Controlled Trials (CENTRAL) and the Cochrane Database of Systematic Reviews (CDSR). Citation tracking and searching the references lists of included studies was also undertaken. Grey literature was searched using the OpenGrey database, internet searching and personal knowledge. An updated search was undertaken in June 2016. Review methods Studies meeting the following criteria were eligible for inclusion; (i) used qualitative data collection and analysis methods; (ii) full-text was available in English; (iii) included adult patients who require oral dosage forms to be modified to meet their needs or; (iv) carers or healthcare professionals of patients who require oral dosage forms to be modified. Two reviewers independently appraised the quality of the included studies using the Critical Appraisal Skills Programme Checklist. A thematic synthesis was conducted and analytical themes were generated. Results Of 5455 records screened, seven studies were eligible for inclusion; three involved healthcare professionals and the remaining four studies involved patients. Four analytical themes emerged from the thematic synthesis: (i) patient-centred individuality and variability; (ii) communication; (iii) knowledge and uncertainty and; (iv) complexity. The variability of individual patientís requirements, poor communication practices and lack of knowledge about oral dosage form modification, when combined with the complex and multi-faceted healthcare environment complicate decision making regarding oral dosage form modification and administration. Conclusions This systematic review has highlighted the key factors influencing the knowledge, attitudes and beliefs of patients and healthcare professionals about oral dosage form modifications. The findings suggest that in order to optimise oral medicine modification practices the needs of individual patients should be routinely and systematically assessed and decision-making should be supported by evidence based recommendations with multidisciplinary input. Further research is needed to optimise oral dosage form modification practices and the factors identified in this review should be considered in the development of future interventions.