Zeranol (INNTooltip International Nonproprietary Name, USANTooltip United States Adopted Name, BANTooltip British Approved Name) (brand names Frideron, Ralabol, Ralgro, Ralone, Zerano; developmental code names MK-188, P-1496), or zearanol, also known as α-zearalanol or simply zearalanol, is a synthetic nonsteroidal estrogen of the resorcylic acid lactone group related to mycoestrogens found in fungi in the Fusarium genus and is used mainly as an anabolic agent in veterinary medicine.

[1][2][3] Zeranol is approved for use as a growth promoter in livestock, including beef cattle, under the brand name Ralgro (by Merck Animal Health) in the United States.

[2] Although zeranol may increase cancer cell proliferation in already existing breast cancer,[6] dietary exposure from the use of zeranol-containing implants in cattle is insignificant.

[7] Zeranol may be found as a contaminant in fungus-infected crops.

It is 3 to 4 times more potent as an estrogen than the related compound zearalenone.