Animal advocates envision a world where medical testing on animals is a thing of the past, but how would this affect research on new drugs and treatments?

The U.S. Food and Drug Administration (FDA) has pulled the plug on a nicotine addiction study after four squirrel monkeys involved in the research died.

The remaining monkeys will be placed in a permanent sanctuary home, where they’ll receive long-term care.

Officials at the federal agency also announced they’ll take additional steps to ensure the welfare of animals involved in studies that fall under their oversight.

Although it’s not clear what kind of stand the FDA will take on this practice in general, animal advocates see the move as one step closer to a world where animal testing is a thing of the past.

But if scientists could no longer experiment on nonhuman primates, such as chimpanzees, macaques, and baboons, what would happen to all the research on drugs and other treatments?

Researchers use animals to test new drugs, vaccines, medical devices, and other treatments.

In addition to nonhuman primates, many other types of animals are used in research, including mice, rats, rabbits, cats, and dogs.

The U.S. Department of Agriculture reports that 820,812 animals were used in research in the country in 2016. This includes studies done at public and private institutions. More than 71,000 of these animals were nonhuman primates.

The FDA requires companies to conduct animal studies for many treatments before testing a product in clinical trials in people.

Some researchers, though, question whether animal studies are a good predictor of how a drug will work in people.

A 2000 study found that when it comes to determining if a medication is toxic to people, animal testing is 71 percent reliable.

There’s also been a steady decline in public support for animal research.

A 2015 Pew Research Center survey showed that half of Americans disapproved of animal testing. This is a slight drop from several years before.

It’s not just animal advocates who are pushing for an end to animal testing.

Many researchers and universities have embraced an ongoing reduction in animal research. This is guided by a set of principles outlined more than 50 years ago.

Known as the 3Rs, this strategy focuses on replacing animal research with reliable alternatives, reducing the number of animals used in research, and refining how animals are handled to improve their well-being.

This applies to all animals, not just nonhuman primates.

One example of this is the National Institutes of Health ending its support in 2015 for invasive research of chimpanzees.

A gradual shift away from using animals in research would give scientists time to find suitable alternatives.

But the U.K.-based Wellcome Trust wrote recently that some types of research still heavily rely upon the use of nonhuman primates.

This includes testing the safety of new drugs and medical devices, which is required by regulatory agencies like the FDA.

But it also includes research on infectious diseases, vaccines, neuroscience, eye diseases, and transplanting animal organs or tissues into people, such as pig or cow heart valve replacements.

These are the areas that would be impacted most by a complete ban on research involving nonhuman primates.

Even without a full ban on animal research, scientists continue to search for suitable alternatives to animal testing.

The Wellcome Trust listed four possible avenues of research.

One is using human volunteers, such as in controlled studies of certain flu or typhoid virus strains. Or turning to other species, such as worms or mice genetically altered to be more similar to humans.

Ongoing developments in high-resolution imaging techniques such as MRIs may one day replace some of the brain research currently being done on monkeys and other nonhuman primates.

Finally, there are attempts to create models of human tissues or organs using either human cells or computer simulations — an area that has much ongoing research right now.

“There are several technologies developing that combine reconstructed tissues or cells from different organs together to create a whole ‘system,’” said Erin Hill, co-founder and president of the Institute for In Vitro Sciences Inc., a nonprofit research and testing laboratory that focuses on developing nonanimal methods.

“Many of these tissues or cells are from human origin, which researchers would agree are often more relevant than animal cells,” Hill told Healthline.

Several research groups are working on organs-on-a-chip that can be used to test what effect a new drug might have on people.

The University of Pittsburgh’s Drug Discovery Institute has developed a liver-on-a-chip for testing the toxicity of drugs.

This plastic and glass chip is about the size of a AA battery. Liver cells are grown inside this scaffold with nutrients pumped through to nourish them.

Drugs or chemicals can also be pumped through the channels to see how the human organ would respond to them.

Other researchers are working on similar chips that simulate the intestines, heart, or other organs.

Some scientists hope to one day tie together these many organ models into a complete human-on-a-chip.

This research has attracted the attention of the FDA.

“The FDA has several projects to investigate how these technologies can be utilized for drug development,” Hill said. “These technologies hold the promise of being more human relevant and predictive and are often faster — and therefore cheaper — than animal models.”

Last year, the FDA announced that it started testing whether livers-on-a-chip can reliably show how people might react to dietary supplements, cosmetics, and foodborne pathogens.

The agency also plans to test kidney, lung, and intestine chip models.

Right now, scientists are building general organs-on-a-chip using cells taken from organs or tissues donated to science.

But in the future, they might be able to create personalized systems using cells from a specific person.

Other scientists are working on three-dimensional mini-organs, including an artificial nose for testing the toxicity of inhaled particles, a mini-lung for studying the effects of air pollution, and mini-brains to model larger-than-chip human brains.

Another group of researchers is using the power of computers to create a virtual human that could be used for testing new drugs or treatments.

This model could also allow doctors to map complex surgeries before undertaking them, as well as serve as a simulation-based training tool for health professionals.

The Parametric Human, as it’s been called, would be a computer map of the entire body, including bones, muscles, and connective tissues.

The researchers envision doctors uploading a patient’s personal data into the model, and then running simulations to see how this person might respond to a drug or treatment.

Another computer-based project involves mapping chemically similar substances, which tend to also have similar effects on the human body.

This would reduce the need for animal testing if the toxic effects of a similar chemical are already known.

Before these alternatives can be used in the real world, researchers will need to test them against animal experiments to show that they’re reliable.

If they work, though, they may not only save animals’ lives. They could also be faster, cheaper, and more personalized than current research methods.