We hypothesised that varying the timing of metformin administration before a standardised nutrient load would affect glucose-lowering, and, in this ‘proof-of-concept’ study, we evaluate the effects of metformin administered by intraduodenal perfusion at different time intervals (0, 30 or 60 min) before a standardised intraduodenal glucose load on plasma glucose, GLP-1 and insulin levels in metformin-treated participants with type 2 diabetes. This evidence concerns the gene INS and type 2 diabetes mellitus.