Glivec (imatinib mesylate) has changed the natural history of chronic-phase chronic myeloid leukemia (CML-CP), transforming it into a long-term and manageable disease. At our institution, we treat over 100 patients with CML-CP per year, typically with first-line imatinib therapy. Recently, several healthcare systems and insurance providers have substituted non-branded versions of imatinib that have not demonstrated efficacy or safety comparable to that of imatinib. Here, we analyzed a series of 12 patients who were exposed to non-branded versions of imatinib. Following the switch from branded imatinib to non-branded imatinib, 5/8 patients (63%) experienced treatment failure and 6/8 (75%) experienced severe and recurrent adverse events. All four patients treated with first-line non-branded imatinib therapy experienced resistance or a suboptimal response, and 3/4 (75%) also experienced intolerance. Overall in this small patient cohort, all 12 patients treated with non-branded imatinib therapies failed to meet common treatment milestones and/or suffered recurrent and severe adverse events.