People with severe mental illness (SMI) in Ethiopia chew khat despite advice from their physicians to desist. We wanted to better understand their reasons for khat chewing, including any benefits that they might gain. A qualitative study was conducted involving patients with SMI and their caregivers in Butajira. Reasons given by patients as well as caregivers were more or less congruent: social pressure, a means for survival by improving function, combating medication side effects, to experience pleasure and curbing appetite. These findings will be of value to health workers, caregivers and policymakers alike in improving care and understanding for this patient group. Furthermore, our study indicates a role for future research to explore potentially beneficial effects of khat in this population.