Vegetarian Guide

The Downside to Consuming Animal Products

How Hormones Could Affect Your Health

Every year, approximately 36 million cattle are raised to provide beef for US consumers.1 Two-thirds of these cattle (about 24 million cows) are given hormones to help make them grow faster.2 Although the USDA and FDA claim that the hormones are safe, there is growing concern that hormone residues in meat and in cow manure might be harmful to human health and the environment.

According to expert scientists appointed by the European Union, the use of growth hormones in food animals poses a potential risk to consumers' health.3 The scientists reported that hormone residues found in meat from these animals can disrupt the consumer's hormone balance, cause developmental problems, interfere with the reproductive system, and even lead to the development of cancer.4 Children and pregnant women are most susceptible to these negative health effects.5

Hormone residues in beef are also thought to cause the early onset of puberty in girls.6 This puts girls at greater risk of developing breast cancer and other forms of cancer.7

As a result of these health risks, the European Union has banned the use of growth hormones in cattle and has prohibited the import of hormone-treated beef since 1988. However, despite scientific concern, the United States and Canada continue to allow cattle to be given six hormones - three naturally occurring and three synthetic (man made).8

Scientists are also concerned about the environmental impact of hormone residues that are found in cow manure. When manure is excreted, these hormones can contaminate surface and groundwater, thereby harming local ecosystems. Aquatic ecosystems are particularly vulnerable to the negative impacts of hormone residues; recent studies have demonstrated that exposure to hormones has a substantial effect on the reproductive capacity and egg production of fish.9

Poultry and Hogs

By law, hormones cannot be given to poultry and hogs. But animals can be fed growth enhancers and feed additives in order to make the poultry grow faster. These additives are not considered hormones, but there is concern that they might affect human health.

You also might want to ask if animal protein was fed as an additive or as part of their diet. What you are concerned about is if any of the animal protein fed to poultry or hogs contains hormones. If a chicken, turkey or pig is fed beef or a beef byproduct, that beef could conceivably contain hormones – this is one way hormones are thought to be getting into the poultry supply. It is uncertain whether this type of hormone transmission is affecting human health, so you must decide whether or not this is important to you.

Did you know?

  • According to the Cattlemen's Beef Association, 90% of all U.S. feedlot cattle are hormone implanted.10
  • A study of cows treated with melengestrol acetate (one of the artificial growth hormones approved for use in the U.S.) revealed that 12% of the hormone passed directly through the cows into their manure.11
  • According to the Scientific Committee on Veterinary Measures Relating to Public Health (SCVPH) appointed by the European Commission, “The potential adverse effects on human health from residues in bovine meat and meat products include endocrine, developmental and neurobiological, immunological as well as carcinogenic, genotoxic and immunotoxicological effects…" 12


Despite opposition from scientists, farmers, and consumers, the US currently allows dairy cows to be injected with recombinant bovine growth hormone (rBGH), also known as recombinant bovine somatotropin (rBST). Developed and manufactured by the Monsanto Corporation, this controversial, genetically engineered hormone forces cows to artificially increase milk production by 10 to 15 percent.13

Canada and the European Union have banned the use of rBGH as a result of safety concerns revealed during product testing. However, in the United States, the FDA approved the use of rBGH in 1993 and continues to assure consumers that the hormone is safe for humans and cows.

Studies conducted by Health Canada determined that administration of rBGH is harmful to cows' health; the drug increases the risk of mastitis (an infection that causes painful inflammation of the udders) by 25%, interferes with reproductive functions, and increases the risk of clinical lameness by 50%.14

Since the abnormally high rate of milk production induced by rBGH strains cows' immune systems, the animals are more susceptible to sickness– this leads producers to administer larger doses of antibiotics and other drugs, which increases the risk that trace residues of these drugs will appear in cows' milk.15

Use of rBGH is also linked to the growing threat of mad cow disease. Since cows injected with rBGH produce more milk, their bodies need additional protein and high-energy foods. This dietary requirement is often satisfied by supplementing feed with increased amounts of animal protein. Since mad cow disease can be spread to cattle through consumption of infected animal byproducts, increased consumption of animal protein puts dairy cows at a greater risk of contracting the disease.

There is also concern that the FDA failed to conduct thorough testing of rBGH before approving the controversial drug. Critics argue that the hasty approval was the result of pressure placed on the FDA by the Monsanto Corporation and its powerful lobbyists. In fact, Dr. Richard Burroughs, a senior FDA scientist overseeing the rBGH safety studies, claims that he was fired from the FDA because his concerns about the safety of rBGH delayed the approval process.16 In 2003, approximately 33% of the 9 million U.S. dairy cows were in herds treated with rBGH.17 The U.S. does not require milk from these cows to bear any special label. While some dairies have pledged not to use the hormone and have created "rBGH-Free" labels for their milk, Monsanto has filed lawsuits against a number of these dairies in order to eliminate the labels and prevent consumers from obtaining complete information about their milk.

Did you know?

  • rBGH is virtually identical to the naturally occurring hormone, BGH. There are no tests to distinguish rBGH from BGH in milk.18
  • A panel of experts appointed by Health Canada to study the impacts of rBGH determined that use of the drug reduces the lifespan of dairy cows.19
  • In 2004, U.S. milk cows produced 170.8 billion pounds of milk. 20


1. Raloff, Janet. “Hormones: Here's the Beef: environmental concerns reemerge over steroids given to livestock.” Science News. Vol 161 #1, p.10. January 5, 2002.

2. Ibid.

3. Duplisea, Bradford. “The Real Dope on Beef Hormones” Canadian Health Coalition. 2001.

4. Ibid.

5. Ibid.

6. Ibid.

7. Ibid.

8. U.S. FDA Center for Veterinary Medicine. “The Use of Steroid Hormones for Growth Promotion in Food-Producing Animals.” FDA July, 2002.

9. Raloff, Janet. “Hormones: Here's the Beef: environmental concerns reemerge over steroids given to livestock.” Science News. Vol 161 #1, p.10. January 5, 2002.

10. Cummins, Ronnie, and Ben Lilliston. “ Beef Hormones, Irradiation & Mad Deer: America 's Food Safety Crisis Continues.” Campaign for Food Safety. June 1999.

11. Schiffer, Bettina, Andreas Daxenberger, Karsten Meyer, and Heinrich H.D. Meyer. “ The Fate of Trenbolone Acetate and Melengestrol Acetate after Application as Growth Promoters in Cattle: Environmental Studies.” in Environmental Health Perspectives. Vol. 109, 11. November 2001. p. 1145.

12. The Scientific Committee on Veterinary Measures Relating to Public Health (SCVPH). Opinion of the Scientific Committee on Veterinary Measures Relating to Public Health: Assessment of the Potential Risks to Human Health from Hormone Residues in Bovine Meat and Meat Products. European Commission. April 1999.

13. Monsanto Corporation. “About POSILAC.” Monsanto Corporation. 2003.
14. Health Canada . Report of the Canadian Veterinary Medical Association Expert Panel on rbST. Health Canada . November, 1998.

14. The Humane Farming Association. Milk Machines: Dangers in the Dairy Industry. The Humane Farming Association. Accessed July, 2004.

15. Ibid.

16. Monsanto Corporation. “Posilac Bovine Somatotrophin by Monsanto – Helping Dairy Farmers Increase Cows' Milk Production: General Information.” 2003.

17. Health Canada.“ Information: Overview of Recombinant Bovine Somatropin (rbST) by Health Canada.” Health Canada. October 1998.

18. Canadian Veterinary Medical Association. “ Report of the Canadian Veterinary Medical Association Expert Panel on rbST.” Health Canada . November 1998.

19. National Agricultural Statistics Service, USDA. “ Milk Production.” USDA. April 15, 2005.

This factsheet was prepared by the Physician's Committee for Responsible Medicine (


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