CYP2C19 and diabetes mellitus: Finally, in this research, the possible effects of untreated diabetes and post-treatment effects of metformin and/or cinnamon consumption on CYP2C19 were examined in diabetic rat isolated perfused liver model by measuring changes in the 5-hydroxy omeprazole-to-omeprazole ratio as an accepted probe for evaluating the CYP2C19 activity (29, 30).