Are There Hormones in US Milk? Separating Fact from Fiction

December 24, 2025 •

4 min read

Approximately 17% of U.S. dairy cows received the synthetic hormone rBST in 2007, but the use of the growth-promoting drug has declined significantly since then, primarily due to consumer preference. The key question, "Are there hormones in US milk?", involves understanding the difference between naturally occurring hormones found in all milk and the controversial artificial ones.

Quick Summary

All milk naturally contains hormones, but the use of synthetic rBST in US milk has dropped considerably due to consumer preference, not safety issues. The FDA considers rBST milk safe, and the majority of milk on the market comes from untreated cows.

Key Points

All Milk Contains Natural Hormones: Every milk, including US milk, naturally contains small amounts of hormones like bovine somatotropin (bST), estrogen, and prolactin, which are part of a cow's normal biology.
Synthetic rBST Use Has Declined: The use of the synthetic growth hormone rBST has become rare in the US dairy industry, largely due to consumer preference and not safety concerns.
rBST is Inactive in Humans: The FDA and other health organizations have affirmed that rBST is biologically inactive when consumed by humans, as it is a protein that is destroyed during digestion.
All Milk is Tested and Regulated: Whether conventional or organic, all milk sold in the U.S. is subject to stringent safety standards and testing, ensuring that it is safe for consumption.
Labels Clarify Production Methods: Consumers seeking to avoid milk from rBST-treated cows can easily find products labeled "rBST-free" or bearing the USDA Organic seal, which prohibits its use.
No Link to Early Puberty: The claim that milk hormones cause early puberty has been debunked by scientific evidence, with childhood obesity considered a more likely factor.

Understanding Hormones in Milk

To understand the issue of hormones in U.S. milk, it's crucial to differentiate between two types: those that occur naturally in all milk and the synthetic versions, primarily recombinant bovine somatotropin (rBST). All living organisms, including plants and animals, naturally produce hormones to regulate growth and biological functions. A glass of milk, therefore, contains a tiny, natural amount of bovine somatotropin (bST), along with other naturally occurring hormones like estrogen and prolactin.

Natural Hormones in Cow's Milk

Bovine Somatotropin (bST): A protein-based growth hormone naturally produced by a cow's pituitary gland that regulates milk production. The natural bST in milk is inactive when consumed by humans, as it is destroyed during digestion.
Estrogen: Milk naturally contains small amounts of estrogen, which can be slightly higher in pregnant cows, as is common in commercial dairy farming. However, research indicates the amount is minimal compared to endogenous human production.
Prolactin: A protein hormone that regulates lactation and is found in milk from many species. In adults, consumed prolactin is broken down into amino acids during digestion and has no biological impact.

The Rise and Decline of rBST

Recombinant bovine somatotropin (rBST), also known as rBGH, is a synthetic version of the naturally occurring bST. The U.S. Food and Drug Administration (FDA) approved its use in 1993 for dairy farmers to increase milk production. Its use sparked significant public concern and consumer backlash, despite FDA assurances of its safety. Over time, consumer pressure led to a market-driven phase-out of the hormone. Today, the majority of U.S. milk is labeled as being from cows not treated with rBST, making the use of the synthetic hormone quite rare.

What Health Experts and Regulators Say

Both the FDA and numerous scientific bodies, including the National Institutes of Health and the World Health Organization, have affirmed that milk from rBST-treated cows is safe for human consumption. These organizations state there is no significant difference between milk from treated and untreated cows. They point to several factors to support this conclusion:

Biologically Inactive: As a protein hormone, rBST is not orally active in humans. The pasteurization process further denatures the protein, and any remaining trace amounts are broken down by digestive enzymes.
No Significant Difference: Scientific studies have found no significant difference in the composition or nutritional quality of milk from cows treated with rBST and those that are not.
IGF-1 Concerns: Some concerns were raised about elevated levels of insulin-like growth factor (IGF-1) in rBST-treated cows, which is also naturally present in all milk. However, the IGF-1 levels in milk are very low, and its biological activity in humans after consumption is considered negligible.

Comparing Milk Options: Conventional, rBST-Free, and Organic

Understanding your choices at the grocery store can help you make an informed decision based on personal preferences. The primary difference between these milk types, concerning hormones, lies in the use of supplemental rBST.


Feature	Conventional Milk	rBST-Free Milk	Organic Milk
Use of rBST	Legally permitted, though now rare due to market demand.	Explicitly labeled as being from cows not treated with rBST.	Prohibited by USDA organic regulations.
Natural Hormones	Contains naturally occurring bST, estrogen, etc..	Contains naturally occurring bST, estrogen, etc..	Contains naturally occurring bST, estrogen, etc..
Antibiotic Use	Antibiotics may be used to treat sick cows, but milk is rigorously tested to ensure no residues enter the supply.	Same residue testing protocols as conventional milk.	Antibiotics are prohibited, but sick cows can be treated and removed from the organic herd.
Feeding Practices	Cows are fed conventional grain and forage.	Similar to conventional, but without rBST.	Cows are fed organic feed.

Reading Labels for Reassurance

For consumers concerned about rBST, reading product labels is the most effective way to choose milk from untreated cows. Many labels explicitly state “rBST-free,” “rBGH-free,” or “from cows not supplemented with rBST”. The presence of the USDA Organic seal also guarantees that the milk comes from cows not treated with any growth hormones. It is worth noting that the FDA mandates a disclaimer on rBST-free products clarifying that no significant difference has been shown between milk from treated and untreated cows.

Dispelling Common Misconceptions

Several myths have persisted regarding the use of hormones in milk. For example, the claim that milk hormones cause early puberty is not supported by credible scientific evidence. Many pediatric nutrition experts point to rising rates of childhood obesity as a more likely factor for earlier maturation, not milk consumption. Likewise, the term “hormone-free” on food items is misleading marketing, as all food from plants and animals contains natural hormones. Plant-based foods like soybeans or cabbage can even contain much higher levels of certain hormones (phytoestrogens) than milk.

For further information on the FDA's stance and review process regarding rBST, the FDA website is a useful resource: Bovine Somatotropin (bST).

Conclusion: Making an Informed Choice

In conclusion, the question of whether there are hormones in US milk has a nuanced answer. All milk naturally contains trace amounts of hormones, a biological reality for any dairy product. The use of the synthetic hormone rBST, however, is a separate issue. While historically approved for use, rBST has been largely phased out of the U.S. milk supply due to consumer demand, not because of demonstrated safety risks to humans. Federal regulations and extensive research from major health organizations confirm that milk from rBST-treated cows is safe to drink, with the protein being biologically inactive in humans. Consumers can confidently choose between conventional, rBST-free, and organic milk by reading labels, knowing that all are held to high safety standards. Your choice depends on your preference regarding the production process, not on scientifically supported health concerns.

Frequently Asked Questions

Yes, all milk, whether from cows, humans, or other mammals, naturally contains hormones. These hormones are a normal part of the animal's biology and are present in trace amounts.

While the FDA has approved rBST for use, its application has significantly declined over the past decade due to consumer demand. The majority of milk sold in the U.S. today is labeled as being from cows not treated with rBST.

Yes, the FDA and other major health organizations have consistently reaffirmed that milk from cows treated with rBST is safe and wholesome for human consumption. The synthetic hormone is not orally active in humans.

No, scientific studies have shown there is no significant difference in the composition or nutritional quality of milk from cows treated with rBST and those that are not.

Yes. If a carton is labeled "rBST-free," "rBGH-free," or "from cows not supplemented with rBST," it means the milk was sourced from untreated cows. The USDA Organic seal also guarantees no growth hormones were used.

No credible scientific evidence supports the claim that hormones in milk cause early puberty. The minute amounts of hormones in milk are not enough to affect human development, and obesity is considered a more likely contributing factor to early maturation.

Not exactly. While all organic milk is rBST-free, the reverse is not always true. Organic certification requires compliance with many other standards, including feeding and living conditions for the cows, not just the absence of supplemental growth hormones.