Sulfonylureas were the first widely used oral hypoglycemic medications. They are insulin secretagogues, triggering insulin release by direct action on the KATP channel of the pancreatic beta cells. Eight types of these pills have been marketed in North America, but not all remain available. The "second-generation" drugs are now more commonly used. They are more effective than first-generation drugs and have fewer side effects. All may cause weight gain.

Sulfonylureas bind strongly to plasma proteins. Sulfonylureas are only useful in Type II diabetes, as they work by stimulating endogenous release of insulin. They work best with patients over 40 years old, who have had diabetes mellitus for under ten years. They can not be used with type I diabetes, or diabetes of pregnancy. They can be safely used with metformin or -glitazones. The primary side effect is hypoglycemia.

- First-generation agents
o tolbutamide (Orinase)
o acetohexamide (Dymelor)
o tolazamide (Tolinase)
o chlorpropamide (Diabinese)

- Second-generation agents
o glipizide (Glucotrol)
o glyburide (Diabeta, Micronase, Glynase)
o glimepiride (Amaryl)
o gliclazide (Diamicron)