FDA Announces Phase?Out of Animal Testing, Reminds of an Old Case

On April 10, 2025, the U.S. Food and Drug Administration (FDA) issued an announcement stating that for monoclonal antibody therapies and other classes of drugs, more effective and human?relevant new methods will be adopted in the future to replace traditional animal experiments. The goal is to improve drug safety, accelerate the review process, reduce animal testing, lower R&D costs, and ultimately bring down drug prices. These new methods include AI?based computational toxicity models, in vitro cell?line and organoid toxicity testing—collectively referred to as “new methodologies.” This plan will take effect immediately for Investigational New Drug (IND) applications. FDA’s newly appointed Commissioner, Dr. Makary, said that for patients, this means a more efficient development pipeline, because human?based testing systems can more accurately predict real?world efficacy, thereby further enhancing safety margins. For animal welfare, this marks an important step toward ending the use of laboratory animals in drug testing; with the widespread adoption of these methods, tens of thousands of animals each year—including dogs and primates—will be spared from experimental suffering.

Researchers in the field of new drug development are well acquainted with “animal testing.” In 1938, the U.S. Congress passed the Federal Food, Drug, and Cosmetic Act, which for the first time made animal testing a prerequisite for a new drug’s entry into clinical trials and approval—nearly 90 years ago. Under current domestic and international regulations, animal experiments remain an indispensable step for moving drugs from the laboratory into clinical use. Through animal studies, researchers can evaluate a drug’s safety, efficacy, and dose–response relationships, providing scientific justification for human trials and minimizing potential risks to ensure participant safety. Animal studies typically include pharmacology, pharmacodynamics, pharmacokinetics, and toxicology (acute toxicity, repeat?dose toxicity, genetic toxicity, reproductive toxicity, carcinogenicity, etc.).

Although animal testing is currently an essential part of preclinical drug development, it has long been controversial—some even regard it as a “necessary evil” in the history of pharmaceutical development. According to incomplete statistics, about 100 million vertebrate animals worldwide undergo various experiments each year. Such massive demand has given rise to numerous companies specializing in preclinical animal studies—Charles River Laboratories and LabCorp in the U.S.; WuXi AppTec and JOINN Biosciences in China; and Clea Japan and Shin Nippon Biomedical Laboratories (SNBL) in Japan. These companies earn enormous profits from experimental animals, yet behind those profits lie countless living beings. Even more regrettable, inter?species differences mean that animal models cannot predict human trial outcomes with 100% accuracy. Many drugs that appear safe and effective in animals perform poorly in human trials, leading to wasted resources and delays in drug development.

In fact, this is not the FDA’s first proposal to eliminate animal testing. In September 2022, the U.S. Senate passed the Modernization of Cosmetics Regulation Act (“FDA Modernization Act 2.0”), which amended the term “preclinical studies (including animal studies)” to “nonclinical studies,” and further defined nonclinical studies as those that “may include animal studies or non?animal, human?biotic test methods such as cell?based assays, microphysiological systems, bioprinting, or computer models.” To advance this legislation, in February 2024 Congress introduced the Modernization of Cosmetics Regulation Act 3.0, which explicitly requires the FDA to establish a framework to support nonclinical test methods that do not involve animals during drug development. Although the bill has not yet been formally voted on in the Senate, given the current U.S. stance on animal testing, it is expected to pass smoothly.

But can a new drug developed without animal data truly be safe? On the same day the FDA’s announcement was released, the National Association for Biomedical Research (NABR) immediately voiced objections, stating that no currently available alternative method can fully replace animal experiments in biopharmaceutical research and drug development. This debate brings to mind a notorious old case in pharmaceutical history: the thalidomide tragedy.

In 1960, the rate of birth defects among newborns—especially in Europe—suddenly and alarmingly increased. Affected babies, nicknamed “seal babies,” were born without arms or legs, or with severely shortened limbs resembling flippers. The mortality rate was extremely high; most did not survive past their first birthday, and tens of thousands of infants died worldwide.

At the height of the Cold War, and since the U.S. had not seen large numbers of such cases, many conspiracy theorists blamed a new American biochemical weapon. However, as investigations deepened, Dr. Widukind Lenz traced the cause to a drug taken by pregnant women—thalidomide. Thalidomide was initially synthesized in 1953 by Chemie?Grünenthal in Germany as an antimicrobial agent but was abandoned when it showed no antibacterial activity. Later, researchers discovered its central nervous system effects and its ability to suppress pregnancy?related nausea. Marketed as a “miracle anti?nausea” drug under the brand name Contergan, it became wildly popular.

In September 1960, Contergan’s U.S. distributor, Richardson?Merrell, submitted a New Drug Application to the FDA. Although thalidomide had already been approved in over 20 countries, FDA reviewer Frances Oldham Kelsey insisted that the pharmacological data from animal studies did not match human outcomes and that existing toxicology data were insufficient. She required Richardson?Merrell to provide additional animal studies to demonstrate that the drug would not harm fetuses. Her decision proved immensely wise and professional. Subsequent research revealed that while thalidomide showed weak teratogenic effects in commonly used rodent models, it was highly teratogenic in primates, including humans. In October 1962, in recognition of her outstanding contribution, President John F. Kennedy awarded Dr. Kelsey the President’s Award for Distinguished Federal Civilian Service—the highest honor a U.S. civil servant can receive.

The thalidomide tragedy directly led to the passage of the Kefauver?Harris Amendment, the cornerstone of modern drug review processes, which formally divided drug development into preclinical and clinical phases. Influenced by this event, the FDA added mandatory teratogenicity testing requirements: studies must be conducted not only in healthy animals but also in pregnant animals throughout the entire gestational period, and in at least two species—one rodent and one non?rodent. Thus, preclinical animal testing gradually evolved into today’s mature system and has become the most powerful safeguard for clinical trial participant safety. 

Now, with the FDA’s announcement to phase out animal testing—a practice that has served human health for nearly 90 years—the future of these animal studies remains uncertain.