Medtronic is at the cutting edge of artificial pancreas development, and its MiniMed 670G was so hotly anticipated that in the run-up to its launch diabetes patients put off replacing their devices. But data presented at the annual meeting of the Endocrine Society suggest that it might have an Achilles heel in terms of its usability. Doctors at the Boston Children’s Hospital gave the device to 93 patients with type 1 diabetes aged between six and 25, who had previously used a separate insulin pump and continuous glucose monitor. Nearly 40% – 35 patients – stopped using the device within nine months, stating that it required too many calibrations or did not stay in automatic mode. Other reasons patients gave for discontinuing use included frequent alarms, premature sensor failure, skin adhesion problems and sensor supply issues. Among the 58 patients who did keep using the 670G, the amount of time in auto mode correlated with reductions in blood sugar, showing that when the system works, it does what it should. Medtronic has already tweaked the system to improve its performance, but the group must hope that these discontinuation rates are not mirrored across the 670G’s customer base.