In the middle of the Caribbean Sea, over 1,000 rhesus macaques live on an island that measures less than a tenth of a mile across. Descendants of a monkey colony imported from India 86 years ago sunbathe, climb trees, and wade in the ocean on Puerto Rico’s Isla de los Monos.

The island serves as a 38-acre open-air laboratory, with these semi-wild macaques as subjects. The monkeys offer a tantalizing opportunity for scientists hoping to observe animal behavior as close to the wild as they can get, while also having ready access to the monkeys’ brains, bodies, and genes. That often means killing them.

One morning in 2021, researchers transported a monkey, like thousands before him, to a laboratory at the Caribbean Primate Research Center (CPRC) at the University of Puerto Rico less than 50 miles away. “We watched him die,” former research assistant Alyssa told me in a video call last summer. “And then we did what we always do, which is take him apart.” (Vox has changed her name to protect her from retaliation.) Killing and dissecting monkeys — up to seven per day, she remembers — was part of the lab’s standard protocol.

During the culling season in the fall, hundreds of monkeys are killed to control the population of the tiny island. Rather than let their bodies go to waste, Alyssa’s team dissected them, meticulously preserving their muscles, organs, and brains for studies attempting to connect the monkeys’ social lives to their anatomy and genetics.

Alyssa joined the lab in 2021, after graduating college. Before accepting the job, the lab’s principal investigator called her, asking whether she was comfortable with blood. She said yes — she wasn’t squeamish, and had no trouble dissecting frogs and lamb hearts in school. “It didn’t raise any flags for me at all,” she said.

Alyssa’s soon-to-be boss then described perfusion, a euthanasia procedure where, in their lab, a deeply anesthetized monkey is strapped to a table and pumped with saline and preservatives while their blood is pumped out. This preserves the animal’s tissue for study after death. But, Alyssa said, he left out that the researchers would be witnessing living animals die in front of them, “no matter whether it was old, whether it was an infant…” She paused. “We dissected infants.”

Every day, Alyssa watched at least one monkey die on an operating table, before she would immediately start cutting into it. Her job was to carefully separate all of the organs and tissues and store them in a freezer, preserving them until other scientists could analyze them. She wore a specially fitted mask to avoid breathing in bone dust while sawing through skulls.

How I reported this

From day one of my Future Perfect fellowship — exactly one year after my last day working with monkeys as a PhD student — I knew I wanted to write this story. I was sure I wasn’t alone in my post-animal research angst, but I wanted to find others willing to share their experiences with me.

I ended up speaking with nearly a dozen people, these interviews capturing all of my own unspoken feelings: that it’s impossible to explain what one sees in these facilities, but dissociating from it is impossible, too.

Over the next several months, I weaved pieces of these conversations together with my reporting on mental health in academia and animal testing regulation. The nuance of this piece was tricky, and my goal throughout was to highlight flaws in the academic system without undermining the value and necessity of the research itself.

I worked with a team of editors, fact-checkers, and lawyers to get there. (The first draft of this piece was nearly twice as long as what you’re reading now!)

As she settled into her new routine, she realized just how difficult her day-to-day life would be to explain to outsiders. “The thing that was so crazy to me,” Alyssa said, “was no one else will know what has happened here.”

She vented about the monkeys on her daily calls to her boyfriend some 1,600 miles away back home. But he couldn’t handle story after story of relentless, visceral gore, so Alyssa turned to her therapist. After crying over the phone, she waited for the calm reassurance she’d come to expect. Instead, her therapist told Alyssa that she was really worried for her mental health. “I surprised myself with how alone I was feeling,” she remembered.

The night terrors began when she came back home. Culling season was over, but Alyssa woke up to panic attacks for months. She’d flinch whenever someone approached her from behind at work or surprised her in public. Symptoms piled up for months before a psychiatrist named what she was experiencing: post-traumatic stress disorder.

A multimedia artist as well as a scientist, Alyssa started creating art inspired by the necropsies seared into her memory — anything to make the images visible to the outside world. During our video call, she reached out of frame and pulled out a life-sized crochet replica of a macaque’s gastrointestinal system.

In the necropsy lab, Alyssa cut each monkey’s gastrointestinal tract from rectum to esophagus, picked it up with triple-gloved hands, and weighed it — part of their standard protocol for collecting and preserving tissues after dissection. An adult macaque’s intestines can be over a dozen feet long, and weigh a good deal more than a ball of yarn. To make the plush guts feel as hefty as she remembered, “I put beads inside them,” she said, “so when you lift it up, it would feel like what you would do every day.”

“I made three: a big, a medium, and an infant-sized.” Alyssa said, holding the tiniest replica, a fuzzy marble-filled snake, to the camera. “I was obsessed with describing to other people what we had seen in that place.”

Alyssa’s experience is anything but rare. Animal research, while largely hidden from public view, is widespread across the life sciences. Animals are used in everything from safety testing for medicines, cosmetics, and pesticides to exploring open-ended questions about how the mind and body work. The drugs we take, the products we use, and the medical breakthroughs we celebrate have been made possible in large part by lab animals and the people who, in the name of science, kill them.

While it’s difficult to find the exact number of scientists, veterinarians, and animal caretakers working in research facilities, we know that somewhere around 100 million animals — mice, rats, dogs, cats, rabbits, monkeys, fish, and birds, among others — are used for research and testing worldwide each year. Between 2011 and 2021, the US National Institutes of Health (NIH) provided $2.2 billion in grants for an estimated 4,000 research projects involving animals.

Animal research is traumatic — obviously for the animals unlucky enough to be involved, but also for many of the humans tasked with harming them. Yet from day one, institutions teach animal researchers that expressing discomfort is akin to weakness, or tantamount to dismissing the value of science altogether. To compete for increasingly rare tenure-track jobs, graduate students and postdocs have no choice but to learn to suppress their emotions and get the work done. Principal investigators, senior scientists who direct animal research labs, often don’t care whether inserting electrodes into a conscious, chronically ill monkey’s brain makes you squeamish. If you can’t handle the heat, they say, get out of the kitchen.

“The costs have always been out there,” bioethicist and former animal researcher John Gluck said. “They’ve just been completely ignored.”

I would know. I spent thousands of hours immersed in the world of researching monkeys (known in the scientific community as NHPs, or nonhuman primates), attempting to study how the brain weighs options during decision-making. In 2023, I graduated from the University of California Berkeley with a PhD in neuroscience, questionable data, zero academic publications, and an intense combination of guilt, rage, and burnout that I’m only just beginning to process.

It’s not clear exactly how many researchers suffer mental health consequences from their work, and it’s impossible to disentangle the psychological side effects of harming animals from those of trying to survive in an unforgiving, underpaid, and poorly regulated workplace. I do know that many people I know who worked in an animal research facility, myself included, left feeling broken. “Everybody that I know has horror stories,” Alyssa agreed.

In an emailed statement, CPRC told Vox that it is “deeply committed to supporting our researchers’ mental health and well-being,” and that its researchers are encouraged to seek mental health resources. “As an organization, we remain steadfast in our commitment to upholding the highest ethical, safety, and compliance standards. Our operations align with all applicable federal and institutional guidelines. We actively foster a professional, respectful, and collaborative environment where researchers can openly discuss challenges and seek support,” the statement said.

Academic institutions have long avoided talking openly about the trauma of animal research. In part, they’re afraid that acknowledging it might invite scrutiny from animal rights activists and undermine the public’s already damaged trust in science. The reality is that it’s easier to downplay the emotional toll of animal testing than to confront the ethical and logistical challenges of dealing with it, given just how central it is to biomedical research.

Now, as the Trump administration wages an unprecedented war on scientific institutions, this might feel like a particularly sensitive time to air uncomfortable conversations about painful aspects of science out in the open. But the scientific community can no longer avoid hard conversations about the psychological costs borne by young scientists. If universities and funding agencies admit that there’s a problem, they can take meaningful steps — like providing better mental health resources and investing in non-animal research methods — to improve conditions for everyone.

But if young researchers are left to suffer in silence, it is science itself that will suffer, as bright, empathetic minds turn away from some of the most important questions in research — or worse, leave the field altogether.

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