Growth Hormones in Milk

Girls sharing glass of milk
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Growth hormone can indeed be found in all forms of cow's milk. Bovine growth hormone (bGH), also known as bovine somatotropin (bST), is a protein that's naturally produced by the pituitary gland of cows that leads to the production of milk.

Some milk products contain rbGH (sometimes called rbST), a synthetic recombinant bovine growth hormone given to cows to help them make more milk. Some parents are concerned that this added growth hormone can cause health problems in kids.

Concerns About Growth Hormones in Milk

Artificial growth hormones in milk are generally considered safe by the Food and Drug Administration (FDA) and the World Health Organization (WHO) for a couple of reasons. First, studies show that the total amount of bGH in milk with added hormones and milk without them is about the same. Plus, even though bGH does get passed from dairy cows into their milk, humans don't absorb it. What's not inactivated by heat during pasteurization breaks down in our digestive tracts.

Still, since dairy companies started giving rbGH to cows in the 1990s, people have speculated that it might be linked to certain health issues that are on the rise, including early puberty, cancer, and antibiotic-resistant infections. Here is what we know:

Early Puberty

Initial suspicions that rbGH is linked to early puberty (precocious puberty) had a lot to do with timing. The first studies showing that the average age of puberty is earlier than in prior generations emerged around the same time milk made from cows fortified with rbGH hit the market.

Many studies have now debunked the theory that early puberty is caused by growth hormones in milk. Research now points to improved nutrition and a rise in childhood obesity as probable reasons for why many kids are starting puberty at early ages.

One problem with the theory is that growth hormone is not a steroid hormone that influences sexual development, like estrogen. Even kids who get daily injections of human growth hormone for short stature and other medical conditions don't start puberty early.


IGF-1 is a naturally occurring hormone in both cattle and humans that's linked to cell development. For reasons that aren't fully clear, IGF-1 levels are slightly higher in milk from cows treated with rbGH. IGF-1 is not destroyed by pasteurization, either.

Limited research has suggested that people who have high levels of IGF-1 may be at higher risk for developing certain cancers. One study has shown that drinking low-fat milk increases circulating IGF-1 levels in men, but actually has a protective effect against colon cancer.

Ultimately, the amount that we absorb from a typical daily consumption of milk is a tiny fraction—less than 1%—of the IGF-1 that our bodies naturally produce. The American Cancer Society calls research linking IGF-1 and cancer "inconclusive" and does not officially recommend against people drinking milk with added hormones.

Antibiotic Resistance

Cows who are given rbGH have a small added risk of developing mastitis, which is usually treated with antibiotics. This concerns some scientists, since antibiotic use in animals contributes to the rise of antibiotic-resistant bacteria. When these resistant strains start to spread, antibiotics commonly used to treat humans become less effective.

To help curb this, the FDA has placed limits on dairy farmers' antibiotic use in cows, and milk is now regularly screened during processing. Still, research has shown that up to 60% of non-organic conventional milk, which is more likely to contain rbGH, contains antibiotic residues—though mostly in trace amounts.

Although health experts tout its nutritional benefits and strongly encourage its consumption, cow's milk intake has been steadily declining in the U.S.

Avoiding Growth Hormones in Milk

Whatever you think about growth hormones in milk, it is now fairly easy to avoid them if you want. Despite early popularity of the use of rbGH to boost milk production, only 17% of dairy cows in the U.S. are now being treated with the synthetic hormone.

The FDA has never required special labeling on milk from cows treated with growth hormones, stating that it does not have the authority to require such a food label since milk from treated and untreated cows is materially the same. However, dairy producers who don't use growth hormones do have permission to label their dairy products as being "without" or "free of" rbGH or rbST.

People who want to avoid milk from cow's that are treated with synthetic growth hormone can:

  • Look for an "rbGH-free" or "rbST-free" label: That's fairly easy, as such dairy products are widely available in most chain grocery stores, including Costco, Kroger, Safeway, and Walmart.
  • Buy organic milk: Studies show higher bGH and IGF-1 levels in conventional milk than organic milk.
  • Choose a fortified milk alternative: For families avoiding dairy, the American Academy of Pediatrics recommends fortified soy milk, which contains essential vitamin D, calcium, and other essential nutrients in amounts that are equivalent to cow's milk.

If you avoid milk but consume other dairy products, including cheese, yogurt, and ice cream, keep in mind that they too could be made with milk from cows treated with synthetic growth hormone. Many non-milk dairy products also carry "rbGH-free" or "rbST-free" labels.

9 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Food and Drug Administration. Bovine Somatotropin (bST).

  2. World Health Organization. Evaluation of certain veterinary drug residues in food. Seventy-eighth report of the joint FAO/WHO expert committee on food additives

  3. Synovitz L, Chopak-Foss J. Precocious puberty: Pathology, related risks, and support strategiesOJPM. 2013;03(09):504-509. doi:10.4236/ojpm.2013.39068.

  4. Albin A-K, Ankarberg-Lindgren C, Tuvemo T, Jonsson B, Albertsson-Wikland K, Ritzén EM. Does growth hormone treatment influence pubertal development in short children? Horm Res Paediatr. 2011;76(4):262-272. doi:10.1159/000329743.

  5. American Cancer Society. Recombinant bovine growth hormone.

  6. Ma J, Giovannucci E, Pollak M, et al. Milk intake, circulating levels of insulin-like growth factor-i, and risk of colorectal cancer in menJNCI Journal of the National Cancer Institute. 2001;93(17):1330-1336. doi:10.1093/jnci/93.17.1330.

  7. Welsh JA, Braun H, Brown N, et al. Production-related contaminants (Pesticides, antibiotics and hormones) in organic and conventionally produced milk samples sold in the USAPublic Health Nutr. 2019;22(16):2972-2980. doi:10.1017/S136898001900106X.

  8. Food and Drug Administration. Interim guidance on the voluntary labeling of milk and milk products from cows that have not been treated with recombinant bovine somatotropin.

  9. Robert Wood Johnson Foundation. Healthy beverage consumption in early childhood: recommendations from key national health and nutrition organizations.

Additional Reading

By Vincent Iannelli, MD
Vincent Iannelli, MD, is a board-certified pediatrician and fellow of the American Academy of Pediatrics. Dr. Iannelli has cared for children for more than 20 years.