ObjectivesTo synthesise contributing factors leading to medicine-related problems (MRPs) in adult patients with cardiovascular diseases and/or diabetes mellitus from their perspectives.DesignA systematic literature review of qualitative studies regarding the contributory factors leading to MRPs, medication errors and non-adherence, followed by a thematic synthesis of the studies.Data sourcesWe screened Pubmed, EMBASE, ISI Web of Knowledge, PsycInfo, International Pharmaceutical Abstract and PsycExtra for qualitative studies (interviews, focus groups and questionnaires of a qualitative nature).Review methodsThematic synthesis was achieved by coding and developing themes from the findings of qualitative studies.ResultsThe synthesis yielded 21 studies that satisfied the inclusion and exclusion criteria. Three themes emerged that involved contributing factors to MRPs: patient-related factors including socioeconomic factors (beliefs, feeling victimised, history of the condition, lack of finance, lack of motivation and low self-esteem) and lifestyle factors (diet, lack of exercise/time to see the doctor, obesity, smoking and stress), medicine-related factors (belief in natural remedies, fear of medicine, lack of belief in medicines, lack of knowledge, non-adherence and polypharmacy) and condition-related factors (lack of knowledge/understanding, fear of condition and its complications, and lack of control).ConclusionsMRPs represent a major health threat, especially among adult patients with cardiovascular diseases and/or diabetes mellitus. The patients’ perspectives uncovered hidden factors that could cause and/or contribute to MRPs in these groups of patients.