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Zeranol FAQ

Originally released: June 23, 2017
Updated: June 16, 2021

What Athletes Need to Know About Zeranol

Following the resolution of a recent case involving zeranol, USADA would like to emphasize that there is an extremely small risk of encountering zeranol-tainted meat in the U.S. and subsequently testing positive in a doping control test.

During an investigation into the circumstances of the case involving zeranol, all the possible sources of zeranol ingestion were thoroughly investigated. USADA consulted with independent meat residue experts, as well as scientific experts at the World Anti-Doping Agency (WADA), while also examining the specific circumstances of ingestion. From these findings, combined with earlier negative tests and the very low levels of zeranol in the athlete’s positive urine sample, USADA determined that a resolution of no fault or negligence was appropriate.

However, we understand that athletes may now be questioning the safety of the U.S. meat supply in relation to zeranol and positive tests. To provide you with more information about this little-known substance, we have answered some important questions about zeranol below:


What is zeranol?

Zeranol is veterinary drug approved for use in livestock in the United States, but it is not approved by the U.S. Food and Drug Administration (FDA) for human use.

While zeranol is a legal growth promotant for livestock in the U.S., the FDA and the U.S. Department of Agriculture (USDA) are also responsible for evaluating the safety of zeranol and regulating its use in agricultural contexts. For example, the FDA and USDA imposed regulations to control the amount of zeranol used for stock farming, and established a maximum average daily intake value for zeranol consumption in humans.

Due to its growth promoting and presumed anabolic effects in humans, zeranol appears on the WADA Prohibited List classified under S1.2 Other Anabolic Agents. For more than 15 years, it has been tested for in routine doping control analysis. Across the millions of urine analyses conducted and reported by WADA since 2003, there have been just six positive tests globally. Over the last 15 years, USADA has also performed more than 100,000 tests, and there has been only one zeranol positive.

In response to the global occurrence of positive tests shown to be the result of contaminated medications and meat, a group of scientific and legal experts made specific recommendations to WADA to establish Minimum Reporting Levels (MRLs) for selected diuretics and anabolic steroids/growth promoters detected in urine samples by WADA-accredited laboratories. Starting June 2021, WADA implemented MRLs for a number of prohibited diuretics (namely, acetazolamide, bumetanide, furosemide, hydrochlorothiazide, torasemide, and triamterene), and livestock growth promotors (namely,  clenbuterol, ractopamine, zilpaterol, and zeranol ), and will continue to evaluate the need for MRLs for additional compounds should they be directly associated with contamination. For certain sports or in certain circumstances, results below the MRLs will trigger an investigation by the relevant anti-doping authority to try to determine the source and circumstances around the ingestion or exposure to the prohibited substance. To read more, please see WADA’s statement.


How prevalent is zeranol residue in meat in the United States?

The USDA Food Safety and Inspection Service (FSIS) monitors levels of various residues in tissues such as muscle and liver through random and targeted sampling. These results are published in the FSIS National Residue Program Red Book. In the latest publication, there was only one reported violation of residue for zeranol, which occurred in 2014 in a sow, not beef cattle.


Is there a way to minimize the risk of a positive drug test in the U.S. due to zeranol?

The risk of a positive doping test from meat contaminated with zeranol is remote. In the U.S., USADA has only seen the single positive test due to zeranol in more than sixteen years.

However, in the event of any positive test for zeranol, we will work diligently with the athlete, as we did in the most recent case, to thoroughly evaluate whether the positive test may have come from zeranol contamination.

If you have any questions or concerns, please contact Athlete Connect at 866-601-2632 or athleteconnect@USADA.org.

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