Miglitol, and other structurally-related iminosugars, inhibit glycoside hydrolase enzymes called alpha-glucosidases. Since miglitol works by preventing digestion of carbohydrates, it lowers the degree of postprandialhyperglycemia. It must be taken at the start of main meals to have maximal effect. Its effect will depend on the amount of non-monosaccharide carbohydrates in a person's diet.
In contrast to acarbose (another alpha-glucosidase inhibitor), miglitol is systemically absorbed; however, it is not metabolized and is excreted by the kidneys.