-Purpose. To determine the risk of clinical trial failure for drugs developed for type-2 diabetes. Methods. Drugs were investigated by reviewing phase I to phase III studies that were conducted between 1998 and February 2013. The clinical trial success rates were calculated and compared to the industry standard. The drugs were classified into GLP-1 receptor agonists, DPP-4 inhibitors, SGLT-2 inhibitors and "Other". The exclusion criteria for drugs in this study: Drugs that were started in phase I studies prior to January 1998 for this indication and drugs whose primary indications were not for the control of blood glucose levels. Results. Data was extracted from clinicaltrials.gov; there were a total of 131 drug candidates that fit our specified criteria, of which 8 received FDA approval. The cumulative success rate for molecules developed for type-2 diabetes is 10%. Small molecules were more successful than biologics. A strong disparity was observed in phase III, with studies that utilised treatment naïve patients having a 40% success rate, compared to an 83% success rate in patients who have had previous anti-hyperglycemic exposure. Conclusions. 1 in 10 drugs that enter clinical testing in this disease will be approved. The DPP-4 inhibitor class of drugs had the highest success rate of all drug classes with a 63% cumulative success rate; while treatment naïve patients carried the greatest clinical trial risk.