As a result, OP-conjugated insulin efficiently permeates through the skin into the blood circulation; transdermal administration of OP-conjugated insulin at a dose of 116 U kg−1 into mice with type 1 diabetes quickly lowers their blood glucose levels to the normal range, and a transdermal dose of 29 U kg−1 normalizes the blood glucose levels of diabetic minipigs. The gene discussed is INS; the disease is type 1 diabetes mellitus.