Do Drug Residues End Up in Meat, Milk, and Eggs? Understanding MRLs and Food Testing Gaps

In Part 1, we broke down how drug use has become a routine part of conventional meat production, and why the system depends on it.

But that understanding naturally leads to an important question:

What happens after those drugs are used?

Do they stay within the animal… or do they carry through as drug residues in the meat, milk, and eggs we eat?

Do drugs end up in our food?

Yes, drug residues can and do make their way into the food we eat. (ref, ref)

This isn’t just theoretical. It’s a biological reality.

When animals are given drugs, those compounds don’t simply disappear. They are absorbed, metabolized, and distributed throughout the body. And in some cases, residues (or their metabolites) can remain in tissues that ultimately become part of the food supply.

What animals are exposed to doesn’t stay isolated. It can carry through to meat, milk, eggs, and other animal products.

While violations do occur each year, modern regulatory programs show that the majority of products test below what regulators consider acceptable thresholds.

But that doesn’t mean residue-free.

“Compliant” does not mean residue-free.

It means levels are below the Maximum Residue Limit (MRL), more on that below.

In fact, ongoing testing continues to detect trace levels of antibiotics, antiparasitics, and other veterinary drugs in meat, milk, and eggs. And studies are finding multiple drug residues within a single sample, highlighting how complex real-world exposure can be.

Drug residues have been documented across a wide range of animal foods (ref), including:

> Meat (beef, pork, poultry)

> Milk and dairy

> Eggs

> Honey and

> Seafood

As one review summarizes (ref):

“Veterinary medications used for disease treatment and prevention may remain in animal-derived foods such as milk, eggs, honey, meat or organs… which could pose a risk to public health.”

Today, more than 200 veterinary drug residues from various classes (antibiotics, antiparasitics, and anti-inflammatories) have been identified across different food products. (ref)

Image from ref.

The presence of residues isn’t surprising, it’s supported by well-understood biological mechanisms.

• > Some drugs, like tetracyclines, can circulate widely in the body and persist in tissues and fluids (ref).

• > Others are excreted into bile and then reabsorbed, allowing them to remain in the body longer than expected (ref).

• > Certain compounds, like tylosin, are poorly biodegradable and can persist in food products such as milk, meat, eggs, and honey. (ref)

• > And some residues, like sulfonamides, remain stable even during freezing or storage, meaning they don’t easily break down once present (ref).

Even after treatment ends, residues don’t always disappear immediately. Antibiotics can still be detected in milk after official withdrawal periods (ref), and drug residues can transfer into eggs and persist long after use (ref, ref, ref, ref).

If regulations exist, why do residues still show up?

In practice, there are several well-documented reasons:

• - failure to follow withdrawal periods (ref)

• - improper or extra-label drug use (ref)

• - lack of awareness about what qualifies as a drug (ref)

• - environmental contamination (feed, equipment, housing surfaces)

• - incomplete cleaning of medicated equipment (ref)

There’s also a knowledge gap within the system itself. As one farmer put it:

“There’s a lack of understanding around antibiotics… I have a friend selling calves as ‘all natural’ who didn’t realize certain drugs were antibiotics.”

Even with regulations in place, the system relies heavily on precise compliance and human execution. And that’s where gaps can occur.

But beyond individual errors, there’s another layer to consider: the limitations of how drug residues are regulated and tested in the first place.

How is food regulated for drug residues?

In the United States, drug residues in food are regulated through a combination of FDA and USDA oversight programs.

But it’s important to understand something upfront: the regulatory standard isn’t zero. It’s what’s legally “allowed.”

These limits are known as Maximum Residue Limits (MRLs): the highest level of a drug or chemical legally permitted to remain in food products like meat, milk, and eggs. MRLs are designed to keep residue levels below thresholds considered safe for human consumption.

They are based on something called an Acceptable Daily Intake (ADI), an estimate of how much of a substance a person can consume daily over a lifetime without significant risk. From there, regulators determine how much of that compound is allowed to remain in specific foods.

For many animal products, there is no continuous on-farm testing. Instead, oversight relies on targeted residue testing programs, random sampling, and inspection at slaughter or processing. Meaning, not every batch of meat is tested. Only a fraction of the products are actually sampled. But if the residues are found to be above legal limits, products can be condemned and then traced back to the source.

Conventional milk is the most tightly monitored food in this drug regulatory system. Every bulk milk tanker is screened before it can be processed, making it one of the most consistently tested foods. Any tanker that tests positive is immediately rejected and discarded. According to the FDA’s 2024 National Milk Drug Residue Database report (ref), over 3.6 million milk samples were tested in a single year, with just 301 testing above the MRL, about 0.008% of samples. In 2024 alone, nearly 10 million pounds of milk were dumped after triggering positive residue tests.

At first glance, this suggests a highly effective system, and in many ways, it is.

But it’s important to understand what this testing is actually designed to detect.

Routine milk screening focuses primarily on common antibiotics, especially beta-lactams, and a limited number of required drug classes. It is not a comprehensive screen for all possible compounds.

In fact, FDA surveys have identified additional drugs in milk that are not routinely tested for (ref), including fluoroquinolones, gentamicin, sulfamethazine, and macrolides. So while every load is screened for certain compounds, not every load is fully analyzed.

Plus, a “negative” test result does not mean a product is completely free of drug residues. It means none were detected above the threshold for the specific compounds being tested. Substances outside the testing scope, or residues present below detection limits, may not be captured.

Eggs are monitored differently, and often less intensively.

In the U.S., egg testing is conducted through programs like the USDA’s National Residue Program and FDA targeted sampling efforts. These programs focus on certain antibiotics, some banned drugs, and a limited set of anticoccidials.

But unlike milk, eggs are not tested batch-by-batch. Instead, testing is based on surveillance sampling, meaning only a portion of the total egg supply is ever directly analyzed. (Similar to meat)

Like most foods in the system, egg testing is targeted rather than comprehensive. It is designed to detect known high-risk compounds and potential violations of regulatory limits, not to measure the full range of residues that may be present.

When researchers go beyond these standard testing methods and use broader, more sensitive analytical techniques, they often detect a wider range of compounds.

Studies have identified residues from multiple drug classes in eggs, including coccidiostats, sulfonamides, macrolides, and even banned substances like nitrofurans.

This doesn’t necessarily mean regulatory MRLs are always being exceeded, but it does show that low-level, multi-compound residues can and do exist.

One of the main limitations of this regulatory system is how these limits are set.

They are established one compound at a time, for one food at a time.

But that’s not how real-world exposure works.

People consume multiple foods, each potentially containing residues from different compounds. So in reality, exposure is cumulative, not isolated.

There is currently no routine system in the U.S. that measures total drug burden across the diet. And there is no standardized way to assess combined exposure to multiple residues at low levels.

Most monitoring programs are designed to detect violations, not to fully characterize what consumers are exposed to over time.

Honey offers an interesting extension of this idea. It is another animal-derived food, yet it is often perceived as pure, natural, and minimally processed. However, drugs are also used in beekeeping to manage disease, and residues have been detected in honey.

Like other animal products, honey is subject to regulation for drug residues, and certain antibiotics used in beekeeping have established limits in some countries. But in the United States, the regulatory framework is less clearly defined. There are no established maximum residue limits for honey, and large-scale, routine surveillance data on finished retail honey products is limited. Most testing tends to be targeted, often focusing on imports or specific violations rather than broad monitoring of the overall supply.

This makes honey a useful example of a broader pattern: drugs can be used, residues can be present, and regulations can exist, yet real-world exposure data remains limited. And in a food that many people assume is untouched, it highlights how these questions extend beyond just meat, milk, and eggs.

Image from ref.

MRLs are also not universal. Different countries set different standards and limits for the same compounds.

A 2025 analysis from the University of Nebraska (ref), comparing U.S. standards to Codex Alimentarius (the international benchmark for food safety), found that U.S. limits for veterinary drug residues are often more lenient than those used by many major trading partners.

The study uses a “stringency score,” where a negative score indicates the U.S. allows higher levels of residues compared to global standards.

Across multiple categories, U.S. standards were found to be less stringent:

• > Beef (−3.00): less strict than 9 of its top 10 export markets, including the European Union, Hong Kong, and Mexico

• > Poultry (−9.07): more lenient than all major trading partners, with large gaps compared to China, Mexico, and Taiwan

• > Pork (−3.05): less strict than countries like China, Japan, and Canada

• > Dairy (−3.87): more lenient across all major export destinations

Meaning, food produced under U.S. standards can legally contain higher levels of certain drug residues than would be permitted in other parts of the world.

(This pattern is also seen in pesticide regulations!)

For some antibiotics, the difference is substantial.

For example, the U.S. allows up to 0.5 ppm of certain tetracyclines in muscle meat, while the European Union sets a much lower limit of 0.1 ppm, a five-fold difference. For other tissues, like liver and kidney, the gap can be even larger.

Not every compound follows this exact pattern, but the broader point remains: different countries draw the line for what is considered “safe” in very different places.

And in some cases, the difference goes even further.

And as discussed previously, some drugs like beta-agonists and growth-promoting hormones used in U.S. beef production are permitted with regulated residue limits, while being completely banned in other countries.

Take ractopamine, a beta-agonist used in pork and beef production. It is approved in the United States, with established residue limits in meat. But it is banned in over 150 countries, including the European Union and China, due to concerns about human health effects and differences in how safety is evaluated.

These differences reflect fundamentally different regulatory philosophies. The U.S. system is largely built around determining what level of exposure is considered acceptable, allowing residues as long as they fall below modeled safety thresholds. The European approach is often more precautionary, placing greater emphasis on limiting or eliminating exposure when uncertainty exists.

So when one country allows a compound at a certain level, and another bans it entirely, it raises an important question…

If the science were truly settled, wouldn’t the standards be the same?

At that point, the conversation shifts. It’s no longer just about whether residues are present. It becomes about how much exposure is considered acceptable, and who gets to decide.

Those decisions don’t just shape regulatory limits.

They shape the structure of the food system itself.

What does independent testing show?

Beyond regulatory monitoring programs, independent studies and targeted testing efforts offer a different lens into the food supply.

Instead of asking whether specific drugs exceed legal limits, these analyses often look more broadly at what is actually present.

And the results can be surprising!

• > A recent analysis of ready-to-eat ham detected 14 different veterinary drug residues across samples. (ref)

• > Antibiotic residues have also been detected in beef labeled “raised without antibiotics.” (ref) What’s notable is that while the USDA approves this label, it does not require routine residue testing to verify it. Instead, the claim is based on production practices and documentation, not consistent end-product testing.

Similar findings have been observed in smaller-scale and local systems.

In one U.S.-based study, researchers purchased beef, eggs, and honey labeled “antibiotic-free” from farmers’ markets in East Tennessee and tested them for common antibiotic residues (ref).

They found:

• - Tetracycline residues in all samples

• - Sulfonamides in every beef sample and many egg samples

• - Erythromycin in all beef and honey samples

Even though concentrations were low, this study shows that residues can still be detected, even in products marketed at farmers markets marketed as ‘antibiotic-free’.

Multiple international studies (ref) have also documented antibiotic residues in eggs:

• - One study found 8.6% of eggs contained residues from 12 different antibiotics

• - Another detected 16 antibiotics in over 30% of samples, with some compounds appearing in up to 84% of eggs tested

• - A third study found 30% of eggs contained antibiotic residues, with some exceeding regulatory limits in that country

• - In backyard systems, detection rates were even higher, with one study finding 73% of eggs contained at least one drug residue

While this reference includes some studies from outside the U.S., they demonstrate a consistent biological reality: when hens are exposed to drugs, residues can transfer into eggs.

It’s also worth noting that the U.S. imports eggs and egg products, though in relatively small amounts.

In 2024, the United States imported $90.3 million in eggs, primarily from Canada ($42.3M), the United Kingdom ($15.6M), and China ($7.49M) (ref). These imports are required to meet U.S. standards, but like domestic products, they are evaluated using targeted, risk-based testing,not comprehensive screening.

Other analyses have looked at finished food products.

A 2023 analysis of fast food items (ref) detected multiple veterinary drugs:

• > 60% of samples contained monensin, an ionophore antibiotic not approved for human use

• > 40% contained narasin, another ionophore used in animal feed

• > One Chick-fil-a sample contained nicarbazin, an antiparasitic and avian contraceptive

In a separate 2026 analysis of military food products (ref), researchers screened for over 130 compounds and detected five veterinary drugs across the ten food samples:

• > Monensin was found in 50% of samples. While approved for limited veterinary use, it is banned for human use as monensin is known to cause cardiac toxicity, weakness, gastrointestinal distress, and sudden death (ref)

• > Trenbolone acetate (a growth-promoting hormone widely used in US beef production) was detected at measurable levels

• > Ractopamine, a growth promoter banned in many countries (ref), was also identified

• > Hydroxy-dimetridazole, a banned antimicrobial, was detected at over 160 ppb in a teriyaki beef stick. Regulatory agencies say these are mutagenic and genotoxic, with studies demonstrating DNA damage, cancer risk and reproductive harm (ref)

• > Nicarbazin was found at trace levels, an antiparasitic drug and avian contraceptive. This has been found in school lunch and fast food testing, suggesting widespread contamination of the food supply

Several of these compounds are not approved for human use and associated with toxicity or regulatory concern. And 4 of the 5 veterinary drugs found are manufactured in China and banned in 160 countries.

Taken together, the above findings don’t necessarily mean that regulatory limits are routinely exceeded.

But they do highlight something important:

When testing expands beyond standard regulatory screens, a wider range of residues is often detected.

This underscores a key distinction: regulatory systems are designed to identify violations, while independent studies often reveal what is simply present.

And those are not always the same thing!

Why this is still an active area of research

Detecting veterinary drug residues in food is still an active and evolving area of research.

While modern testing tools can identify trace levels of antibiotics, beta-agonists, and other compounds, scientists are continuously working to develop more sensitive, accurate, and efficient methods. (ref, ref, ref)

As many research papers note (ref), veterinary drug residues in livestock products remain a persistent food safety challenge, and the rapid expansion of detection technologies shows that this field is still evolving.

Meaning, we are still improving our ability to detect what’s actually present in food, and that means we likely don’t yet have a complete picture of all drug residues that may be present.

Part of the challenge lies in the food itself.

Animal-derived foods are complex biological matrices, meaning they contain fats, proteins, and other compounds that can interfere with detection.

As one paper explains:

“The complexity of animal-derived food matrices… necessitates the development of both efficient pretreatment methodologies and highly sensitive and specific detection technologies.” (ref)

Another notes:

“The egg is a complex matrix and the antibiotic extraction from this matrix is a challenging step in the detection and quantification process.” (ref)

This makes testing more difficult than it might seem. Extracting and accurately measuring residues requires multiple steps, each with potential limitations. (ref)

Even after extraction, analyzing the data presents another layer of complexity.

To address this, new detection strategies are actively being developed (ref, ref, ref), including:

• > Multi-residue screening methods that can detect many compounds at once

• > Biosensors for faster, real-time detection

• > AI-assisted analysis to improve sensitivity and reduce error

• > Detection sensitivity to be able to detect lower concentrations more accurately

All of this points to an important reality: we often think of food testing as definitive, but the science behind detecting drug residues is still evolving.

That doesn’t mean current methods are ineffective.

But it does mean they are not perfect, especially when it comes to identifying multiple compounds at very low levels in complex food systems. Because at the end of the day, widespread drug use is a relatively recent addition to the food system!

Even with regulations in place, there are still meaningful gaps in how these compounds are monitored, measured, and understood.

What does this level of ongoing, low-level exposure mean for human health and for the environment?

In Part 3, we’ll take a closer look.