Nonadherence to treatment is common in patients with chronic psychiatric disorders. Few studies have been conducted in Iran on lack of adherence to medication regimen in patients with severe psychiatric disorders. The present study was carried out with the purpose of gaining insight into the experiences of patients, their family members, and nurses on the medication adherence in patients with severe and chronic psychiatric disorders in selected hospitals in Ahvaz, Iran. A qualitative content analysis study was used in the study and the participants included 7 nurses, 5 patients, and 4 family members. The patients were being treated in psychiatric wards of the hospitals of Ahvaz, in southern Iran. The results of data analysis revealed three main themes: 1) Intentional abandonment of medications; 2) Catalysts of medication discontinuation (including side effects, asymptomatic periods, lack of knowledge of family members, and cultural shame of medication use); and 3) Consequences of medication discontinuation. According to the findings of the study, cultural attitudes play an important role in adherence to treatment regimen among the patients with chronic psychiatric disorders. It is recommended to arrange different programs to improve the situation with an emphasis on improving the general attitude of society towards mental illnesses and the need for regular use of the medications.