For decades, researchers have used animal trials to test prescription drugs and other therapies intended for humans. Regulatory bodies, such as the U.S. Food and Drug Administration (FDA), have even required animal trials before drugs can be cleared for human use. Encouragingly, as of December 2022, animal testing is no longer necessary for FDA approval, though it is up to the FDA’s discretion to discontinue enforcing the former requirement. Researchers assert that experiments on animals have been vital to drug development. They also claim that alternatives to animal testing, like organ chip technology and computer modeling, are not yet viable replacements.

However, recent debates about experiments performed on animals have called this practice into question. Because it is unclear how often and to what extent animal studies predict humans’ responses to medications or treatments, researchers may be wasting funds, time, resources, and animals’ lives on unnecessary experiments. This study assessed: 

• How often animal studies translated to human trials and FDA-approved treatments
• How long animal experiments took to advance to human trials
• How consistently results of animal studies reflected outcomes in humans 

Researchers did keyword searches in three databases, filtering for animal studies, translation of medical interventions from animals to humans, and systematic reviews. They defined translation as “the process of turning observations from animal experiments into interventions that improve the health of human individuals and the public.” 

Out of the 5,278 articles they found, the authors selected 122 articles for qualitative analysis and 62 articles for quantitative analysis. These articles covered 4,443 animal studies and 1,516 clinical studies. The selected studies had to be systematic reviews or meta-analyses that investigated how at least one medical intervention used with animals could translate to treating human illnesses, and the researchers used 11 criteria to assess the quality of the studies. 

Researchers determined how long it took for animal studies to progress to human trials by reviewing the dates of the first animal and human studies associated with each treatment. They used narrative summaries and descriptive statistics to understand how many animal studies translated to human application. And finally, they performed a meta-analysis to track how many animal studies shared positive outcomes with human studies. 

The results revealed that 50% of animal experiments progressed to human studies and 40% of animal experiments resulted in randomized control trials (RCTs). Despite the translation rate to humans, only 5% of the studies gained approval from regulators. 

The translation rate for treatments between animals and humans differed depending on the disease type. Treatments for musculoskeletal diseases had the highest translation rate (100%), RCTs (62%), and regulatory approval (15%). Cancer treatments also had a high rate of translation (73%, 47%, and 20%, respectively). Interventions for circulatory and psychiatric diseases fared the worst. Only 1% of circulatory treatments gained FDA approval, while no psychiatric treatments did. 

Among interventions that progressed to human studies, the median time frame from animal studies to the beginning of a clinical trial was five years, an RCT was seven years, and FDA approval was ten years. 

The study had several limitations. It looked at systematic reviews of therapies that advanced from animal to human trials. Therapies that didn’t progress past animal studies may be in fewer systematic reviews, meaning this study may have actually overestimated translation rates between animal and human studies. Additionally, the studies selected for analysis may have skewed more positively due to researchers’ motivation to highlight successful outcomes. 

Despite animal studies translating and applying to people, most didn’t receive regulatory approval. The strict standards required to conduct human trials may be responsible for weeding out many treatments tested on animals first. It is also possible that poor study design and low-quality data may be to blame. 

Animal testing may be beneficial in some biomedical cases — for their part, the authors note that, based on their analysis, “contrary to widespread assertions, the rate of successful animal-to-human translation may be higher than previously reported.” However, it neither guarantees that a treatment will be cleared for use in humans nor that the treatment will offer positive outcomes in people. In light of this, advocates should encourage researchers and regulatory bodies to reevaluate animal experiments for diseases with low translation and application rates in humans. Advocates should also support the research, design, and improvement of animal-free testing methods as potentially more accurate and ethical alternatives to animal experiments.