BACKGROUND: Medication non-adherence is a significant public health concern and is prevalent among mental healthcare users. Approximately 65% of patients with severe mental illness do not adhere to their prescribed medication. Medication nonadherence may worsen mental illness and result in poorer clinical outcomes, including frequent relapses and rehospitalisation rates, as well as long time to remission, which may contribute to increased cost of care. AIM: We explored perspectives regarding reasons for medication non-adherence among readmitted psychiatric patients. SETTING: Weskoppies Psychiatric Hospital, Pretoria, South Africa. METHODS: We adopted the social constructivism paradigm for this exploratory qualitative study. Purposive sampling was used to select 15 re-admitted patients, who were nonadherent to their medication. Data were collected through individual semi-structured interviews. The interviews were audio recorded and transcribed. The data were thematically analysed, using the principles of grounded theory. RESULTS: Substance abuse, a lack of family support and poor health literacy were the most common reasons for non-adherence to medication. Other reasons included medication side effects, healthcare system drawbacks and a lack of finances to access healthcare. Some patients did not adhere to their medication because they believed that their mental illnesses were spiritual in origin. CONCLUSION: Multiple factors contributed to patients not adhering to their medication, ultimately resulting in their relapse and readmission. Clinicians should be cognisant of these factors when trying to prevent relapse and readmission. CONTRIBUTION: Clinicians also ought to identify patients who are at risk of not adhering to medication. Targeted interventions should be established for tackling medication non-adherence.