Sulfonylureas or sulphonylureas are a class of organic compounds used in medicine and agriculture. The functional group consists of a sulfonyl group (-S(=O)₂) with its sulphur atom bonded to a nitrogen atom of a ureylene group (N,N-dehydrourea, a dehydrogenated derivative of urea). The side chains R₁ and R₂ distinguish various sulfonylureas. Sulfonylureas are the most widely used herbicide.

Many sulfonylureas are used as herbicides, because they can interfere with plant biosynthesis of certain amino acids.

As herbicides sulfonylureas function by interfering with biosynthesis of the amino acids valine, isoleucine, and leucine, specifically via acetolactate synthase inhibition. Compounds in this class include amidosulfuron, azimsulfuron, bensulfuron-methyl, chlorimuron-ethyl, chlorsulfuron, ethametsulfuron-methyl, cinosulfuron, cyclosulfamuron, ethoxysulfuron, flazasulfuron, flupyrsulfuron-methyl-Na, foramsulfuron, halosulfuron, imazosulfuron, iodosulfuron, mesosulfuron, metsulfuron-methyl, nicosulfuron, oxasulfuron, primisulfuron-methyl, prosulfuron, pyrazosulfuron-ethyl, rimsulfuron, sulfometuron-methyl, sulfosulfuron, thifensulfuron-methyl, triasulfuron, tribenuron-methyl, trifloxysulfuron, triflusulfuron-methyl and tritosulfuron. These are broad-spectrum herbicides that kill plants weeds or pests by inhibiting the enzyme acetolactate synthase. In the 1960s, more than 1 kg/ha (0.89 lb/acre) crop protection chemical was typically applied, while sulfonylureates allow as little as 1% as much material to achieve the same effect.

They are widely used as antidiabetic drugs in the management of diabetes mellitus type 2. They act by increasing secretion of insulin from the beta cells in the pancreas.

Sulfonylureas are ineffective where there is absolute deficiency of insulin production such as in type 1 diabetes or post-pancreatectomy.

Sulfonylureas can be used to treat some types of neonatal diabetes. Historically, people with hyperglycemia and low blood insulin levels were diagnosed with type 1 diabetes by default, but it has been found that patients who receive this diagnosis before 6 months of age are often candidates for receiving sulfonylureas rather than insulin throughout life.

A 2011 Cochrane systematic review evaluated the effects on treatment of Latent Autoimmune Diabetes in Adults (LADA) and found that Sulfonylureas did not improve metabolic control of glucose at 3 and 12 months, even worsening HbA1c levels in some cases, when compared to insulin. The same review did not find improvement of fasting C-peptide following treatment with sulfonylurea. Still, it is important to highlight that the studies available to be included in this review presented considerable flaws in quality and design.

While prior sulfonylureas were associated with worse outcomes, newer agents do not appear to increase the risk of death, heart attacks, or strokes. This is further reinforced by a 2020 Cochrane systematic review which did not find enough evidence of reduction of all-cause mortality, serious adverse events, cardiovascular mortality, non-fatal myocardial infarction, non-fatal stroke or end-stage renal disease when comparing metformin monotherapy to sulfonylureas. This same review also did not find improvement in health-related quality of life.