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Chicken antibiotics: What do antibiotics do to chickens?

When given the option, most people are inclined to buy meat that is marketed as antibiotic-free. The animals raised and slaughtered for these products have theoretically not been given antibiotics, meaning that they haven’t contributed to the growing problem of antibiotic resistance. Unfortunately, this is not necessarily always the case, due to a lack of oversight when it comes to meat labeling. While sick animals should be administered drugs under the care of a veterinarian, and supplements may help promote health, none should be used to promote growth, or to compensate for the filthy, crowded conditions of industrial farms or the poor immune systems of animals with compromised genetics.

Are chickens raised using antibiotics?

Giving antibiotics to chickens raised for food is standard practice on large-scale, industrial chicken farms—even when birds are not sick. Historically, antibiotics have been given to farmed animals in the United States not only to prevent and treat illness but also to promote growth. In 2017, the Food and Drug Administration (FDA) decided that antibiotics important to human medicine could no longer be used solely for the purpose of promoting growth, due to concerns surrounding an increase in antibiotic resistance. In the same year, drugs that were once available for farmers to buy over the counter were transitioned to being available only with a prescription or veterinary oversight. Although ostensibly these drugs can no longer be used for growth promotion, and must be obtained with a prescription or veterinary oversight, chickens are still routinely given antibiotics. According to the FDA, antibiotic overuse continues, and medically important drug sales for livestock are now nearly double those for human medicine.1

Concerns over antibiotic resistance and on-farm antibiotic use has contributed to the explosive sales of meat labeled as “raised without antibiotics,” which is the fastest growing segment of the meat industry. These labels should be approached with caution, however, as they are sometimes blatantly untrue. These claims’ lack of dependability is largely because meat companies marketing “antibiotic-free” animals are not required to prove through testing that those claims are true. Instead meat companies can simply send in paperwork supporting their assertions to the U.S. Department of Agriculture.

What antibiotics are used in poultry?

A number of different antibiotics are given to farmed chickens. Each class of antibiotics has unique characteristics and is purposed for specific end goals. You may have been prescribed a drug off this list to treat an ailment you faced, as many are used in humans as well as farmed animals, increasing concerns about the development of antibiotic resistance.

Aminoglycosides. These drugs are used to control bacterial growth. They work by preventing the synthesis of proteins that bacteria require to grow.

Bambermycins. Drugs in this class prevent the regeneration of the bacterium’s cell wall.

Penicillins. Perhaps the class of antibiotics that the average person is most familiar with, penicillins were the first class of antibiotic drugs discovered. They work by preventing the formation of a bacterium’s cell wall, spilling the contents of bacterial cells.

Cephalosporins. This class of drugs is closely related to penicillin and behaves similarly. Cephalosporins are separated into three different generations, with those in later generations able to treat a broader range of bacteria than those in earlier generations.

Lincosamides. These drugs are useful against bone infections, as they penetrate most tissues extremely well.

Macrolides. Macrolides work by interfering with the production of proteins by bacteria.

Polypeptides. This class of drugs is bactericidal and includes antibiotics effective against E. Coli and Salmonella.

Fluoroquinolones. These synthetic drugs work by preventing bacteria from creating DNA, thus making it impossible for them to multiply. Banned for use in poultry in 2005 in order to reduce the prevalence of fluoroquinolone-resistant Campylobacter in humans, subsequent studies have found that residues of the banned substances in slaughtered poultry persist.

Streptogramins. These drugs are made up of a combination of two separate and unrelated molecules that individually prevent bacteria multiplying but can end infections when used together. The drugs in this class inhibit both the production of proteins and cell wall formation.

Sulfonamides. Also called sulfa drugs, sulfonamide, are synthetic antibiotics that can treat and prevent disease or to promote growth in chickens. Drugs in this class interfere with bacterial RNA and DNA, making it more difficult for bacteria to replicate. Historically, these relatively cheap drugs have been used extensively, increasing incidences of and concerns surrounding antibiotic-resistant bacteria.[2]

Tetracyclines. The drugs in this group prevent bacteria from multiplying, giving the immune system of the impacted organism the opportunity to fight off the infection. Tetracyclines are widely used in agriculture, applied in quantities surpassing almost every other antibiotic family.

What supplements are given to chickens on factory farms?

The drugs given to chickens come in a variety of different forms depending on how they are meant to be administered and what they are meant to accomplish.

Powdered antibiotics

Powdered antibiotics can be added to feed and given to chickens orally. These antibiotics are most commonly used to treat bacterial infections in birds.


The addition of vitamins to the diet of farmed birds is usually done to increase the productivity of the chickens. By consuming supplemental vitamins, birds may be better equipped to fight off infection as they will have stronger immune systems.3


Coccidia is a common parasitic infection of the intestines in animals, including farmed chickens. Coccidiostats treat the infestation. Many conventional diets for poultry include coccidiostats or cocciocides in them.

Other supplements

Concern over rising antibiotic resistance has led some farmers to turn to feed additives such hot red pepper and chicory root powder to replace some antibiotic use.4 These supplements work by supporting good gut health, enhancing the birds’ ability to fight off infection.

What do antibiotics do to chickens?

In industrial farming, widespread application of antibiotics promotes chickens’ growth and prevents infection, but this overuse of antibiotics in animal farming is widely considered to be a significant contributor to the growing antibiotic resistance crisis. This happens when bacterial populations are able to adapt to the drugs—as genes that confer resistance are selected for—until they can ultimately withstand the antibiotics that once would have quickly and easily dispensed with them. Antibiotic resistance is a serious health concern not only for animals but also for people, as it leads to fewer options for treating bacterial infections and diseases.5 The World Health Organization has declared the growing antibiotic, antiparasitic, antifungal, and antiviral resistance crisis “one of the top 10 global public health threats facing humanity.”6 Antimicrobial resistance was associated with nearly 5 million deaths in 2019, and is predicted to grow to 10 million deaths annually by 20507 —more people than currently die from cancer.

What does antibiotic-free chicken mean?

The term “antibiotic-free” may seem straightforward enough, and a 2019 survey found that 53 percent of consumers thought that “antibiotic-free” labeling should mean that no antibiotics of any kind were given to that animal, but unfortunately this isn’t always the case.

How does the FDA regulate the use of chicken antibiotics?

In 2017, the FDA took steps to regulate the use of antibiotics in raising chickens. In that year, the agency decided that some drugs that were once available for over-the-counter use would need veterinary oversight or a prescription from a licensed veterinarian. In the same guidelines, the FDA also stopped the use of medically significant antibiotics for the purpose of promoting growth. However, antibiotics useful for human medicine can still be routinely applied to poultry, ostensibly for “disease prevention”—with the side effect much desired by industry: promoting growth. In practice, it is difficult to draw a distinction between “promoting growth” and “preventing illness” on farms that raise genetically unhealthy animals in conditions where they almost inevitably become ill.

Is antibiotic use on factory farms dangerous for human health?

The heavy use of antibiotics to eradicate bacteria is an issue that spans both human and animal considerations. This is because many of the same antibiotics that are widely given to animals are also used to treat diseases in people. By using drugs so heavily in farmed animals, factory farming increases the likelihood of bacteria forming resistance, making the antibiotics less effective across the board.

What does the CDC say about antibiotic resistance?

The Centers for Disease Control (CDC) recognizes antibiotic resistance as an issue that spans human and animal health concerns. They urge farmers to use antibiotics only as instructed by a veterinarian and to reduce the need for drugs by implementing high animal welfare standards. In reality, however, chickens on industrial farms have undergone decades of genetic modification that have left them prone to health problems. These conditions are covered up by humanewashing campaigns that lead consumers to believe that the chickens they are consuming were healthy and happy while they were being raised.

When antibiotic-free chicken isn’t antibiotic-free

There have been several instances of meat that was supposed to be antibiotic-free containing antibiotics when analyzed, including research published in Science in 2022. Marketing meat as “antibiotic-free” is economically advantageous, as consumers are willing to pay more for meat from animals that have not been given antibiotics. Recently, meat marketed by Whole Foods as “raised without antibiotics” was found to contain residue of an antibiotic. Farm Forward has joined a class-action lawsuit against the grocery chain to hold them accountable.

Is the use of antibiotics in chicken being reduced?

The FDA has consistently advised farmers to use antibiotics judiciously due to the rise in antibiotic-resistant bacteria and the serious concerns it poses for public health worldwide. Since 2011, the total amount of antibiotics sold for use in farmed animals has roughly trended downward. But according to the FDA, antibiotic overuse continues. After a brief decline from 2015–2017, antibiotic sales for livestock have risen for two straight years. Medically important drug sales for livestock are now nearly double those for human medicine.8


The heavy use of antibiotics for chickens on factory farms is contributing to the antibiotic resistance crisis, a serious public health threat for animals and people alike. Sick animals should be treated, but antibiotics should never be used to promote growth or to compensate for filthy conditions and the use of genetically unhealthy animals. Even those chicken products that are labeled as “antibiotic-free” cannot be trusted due to the lack of oversight when it comes to labeling. The best way for the average consumer to avoid antibiotics in chicken and minimize antibiotic use on factory farms is to eat more plants and as little chicken meat as possible, ideally none.



David Wallinga, Eili Klein, and Alisa Hamilton, “U.S. Livestock Antibiotic Use Is Rising, Medical Use Falls,” November 18, 2021, National Resources Defense Council,


C. K. Cheong et al., “Sulfonamides Determination in Chicken Meat Products from Malaysia,” International Food Research Journal 17 (2010): 885–892,


B. Shojadoost et al., “Centennial Review: Effects of Vitamins A, D, E, and C on the Chicken Immune System,” Poultry Science 100, no. 4 (April, 2021),


Mohamed E. Abd El-Hack et al., “Hot Red Pepper Powder as an Alternative to Antibiotics in Organic Poultry Feed: An Updated Review,” Poultry Science 101, no. 4 (April, 2022),


Center for Veterinary Medicine, USDA, “Antimicrobial Use and Resistance in Animal Agriculture in the United States” (USDA, 2022),


World Health Organization, “Antimicrobial Resistance” Fact Sheet, Nov. 17, 2021,


Steven Roach, “FDA and USDA need to get on board with the CDC about reducing antibiotic use in raising animals for food,” Stat, September 19, 2022. Accessible here. See also Maryn McKenna, “Antibiotic Use in US Farm Animals Was Falling. Now It’s Not,” Wired, December 14, 2021. Accessible here.


David Wallinga, Eili Klein, and Alisa Hamilton, “U.S. Livestock Antibiotic Use Is Rising, Medical Use Falls,” November 18, 2021, National Resources Defense Council,