Incretin mimetics are frequently used in the treatment of type 2 diabetes because they potentiate beta-cell response to glucose. Clinical evidence showing short-term benefits of such therapeutics ( e.g., liraglutide) is abundant, however, there have been several recent reports of unexpected complications in association with incretin mimetic therapy. Importantly, clinical evidence on the potential effects of such agents on the beta cell and islet function during long-term multi-year use remains lacking. We now show that prolonged daily liraglutide treatment of >200 days in humanized mice, transplanted with human pancreatic islets in the anterior chamber of the eye, is associated with compromised release of human insulin and deranged overall glucose homeostasis. These findings raise concern about the chronic potentiation of beta-cell function through incretin mimetic therapy in diabetes.