Promising studies are in the news all the time. Some new drug is tested on lab animals and researchers hope that the positive results will translate to human trials. But that doesn't often happen.

Animals are not often good models of human biology. A growing body of scientific literature questions the reliability of animal experimentation and how well it predicts human outcomes.

Neurologist Aysha Akhtar, M.D., M.P.H., a fellow of the Oxford Centre for Animal Ethics, writes in the Cambridge Quarterly of Healthcare Ethics: "Human diseases are typically artificially induced in animals, but the enormous difficulty of reproducing anything approaching the complexity of human diseases in animal models limits their usefulness."

Through her research, Akhtar argues there are three conditions that explain why animal experimentation fails to successfully translate to humans.

1. The effects of the laboratory environment on study outcomes. Animals are typically placed in cold, windowless rooms in confined spaces with artificial lighting and human noises. These unnatural conditions can cause stress and abnormal behaviors, which can have a significant effect on test results.

2. Disparities between human diseases and animal models of disease. Human diseases are artificially induced in animals, but it's difficult to accurately reproduce complex human diseases in animals. Because of the vast differences, the results often don't translate when humans are studied in the same way.

3. Differences in physiology and genetics within a species. Not only do animals differ from humans, they differ from each other. Studies have shown that mice from the same strain, but purchased from a different supplier, can produce different test results.

The business of lab animals

When researchers first started using animals in labs more than a century ago, they were studying the animals, not using them as stand-ins for people, Todd Preuss, an anthropologist at the Yerkes National Primate Research Center at Emory University, tells NPR.

But eventually, scientists began believing rats were the prototypical animal. They believed we could do and learn nearly everything with rats in a lab, Preuss says.

"You could learn about almost any feature of human organization, you could cure almost any disease by studying these animals."

But that wasn't the case. However, many scientific communities and research centers have evolved around the business of mice, rats and other lab animals. Each year, more than 115 million animals are now used globally in scientific experiments or elsewhere in the biomedical industry.

The problems with research

laboratory cages with mice and rats Lab animals can respond differently depending on where their cages are located in relation to light. (Photo: unoL/Shutterstock)

Joseph Garner, a behavioral scientist at the Stanford University Medical Center, tried to conduct identical experiments with colleagues in six different mouse labs in Europe. They used mice of the same age that were genetically identical, yet the results at the various facilities were nowhere near alike. The study was published in the journal PLOS ONE.

Bedding or food may vary between facilities. Some mice may react differently depending on whether they're near the lights or far from illumination. They may even respond differently to their human handlers. Yet, researchers try to make everything identical. Garner draws a more detailed picture for NPR:

"Imagine you were doing a human drug trial and you said to the FDA, 'OK, I'm going to do this trial in 43-year-old white males in one small town in California,'" Garner says — a town where everyone lives in identical ranch homes, with the same monotonous diets and the same thermostat set to the same temperature.

"Which is too cold, and they can't change it," he goes on. "And oh, they all have the same grandfather!"

The FDA would laugh that off as an insane setup, Garner says.

"But that's exactly what we do in animals. We try to control everything we can possibly think of, and as a result we learn absolutely nothing."

Garner and several colleagues wrote an article for Lab Animal, suggesting researchers start looking at lab animals in a different way.

"When we are used to seeing mice in barren standardized environments, with standardized chow, and standardized genetics, referring to them as models not mice or animals, it is easy to fall into the trap of thinking of them more as little furry test tubes than animal patients," the researchers write.

While some researchers (and plenty of animal rights activists) suggest doing away with animal research completely, Garner and his team disagree.

"Discarding animal research entirely is not the answer. When properly used, animal models have incredible value," they write. The key is to treat the animals as patients, not as laboratory tools.

"The worst outcome though, is falling into the trap of thinking not that well-being doesn’t matter, but that animals can’t feel pain, or can’t be fearful, or can’t be depressed."

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.