Oleoyl-estrone (OE), or estrone 3-oleate, is a fatty acid ester of estrone. It is a naturally circulating hormone in animals, including humans. It was studied as a potential weight-loss drug, but failed to show benefit in clinical trials. It was first reported in 1996 to cause a body fat loss effect in rats in the International Journal of Obesity and Related Metabolic Disorders. The animal research has all been conducted by the Nitrogen-Obesity Research Group of the University of Barcelona.

The compound was found to potently induce body-fat loss while preserving protein stores in animals which is the ultimate goal of an anti-obesity agent as body protein loss is an undesired but inevitable (to some degree) side effect of fat loss via calorie restriction.