Elevation of postprandial plasma glucose is correlated with an increase in cardiovascular events, and alpha-glucosidase inhibitors (αGIs) are effective at reducing postprandial glucose levels. In Japan, the αGIs acarbose, voglibose, and miglitol have been available since 1993, 1994, and 2006, respectively. Dipeptidyl peptidase-4 (DPP-4) inhibitors are also effective at reducing postprandial glucose levels, and they have been available in Japan since 2009. A combination therapy of αGI, miglitol, and the DPP-4 inhibitor, sitagliptin, is more effective at decreasing postprandial glucose levels than monotherapy with either miglitol or sitagliptin. Moreover, the combination therapy of miglitol and sitagliptin is more effective at increasing postprandial active glucagon-like peptide-1 (GLP-1) levels than monotherapy. Peptide YY (PYY) has appetite-suppressing and gastric-emptying effects similar to GLP-1. In healthy individuals, miglitol increases the postprandial total PYY; however, combination therapy of miglitol and vildagliptin does not change postprandial total PYY levels. αGIs are typically prescribed to be taken just before a meal, which can result in decreased drug adherence. Different patterns of αGI intake were examined, and the results showed that miglitol or acarbose administration after a meal is effective. The effects of taking miglitol dissolved in water during a meal appeared to be similar to that of taking miglitol as a tablet just before a meal. The long-term effects of taking miglitol dissolved in water should be evaluated in future studies. αGIs may be effective even when they are not taken before a meal, and a more flexible administration may improve drug adherence.