Secretly filmed footage from inside two regulated UK testing facilities has exposed the hidden reality behind the safety trials required before new weight-loss drugs – and countless everyday medicines – can reach pharmacy shelves. The images show long-tailed macaques restrained while a rubber tube is forced down their throats in a procedure known as oral gavage, delivering anti-obesity medication directly into their stomachs. The animals’ distress is unmistakable: they struggle, cry out and scream as the tube is pushed into place.
The unprecedented footage supplied to The Mail on Sunday was secretly filmed by a lab worker at two UK testing plants. Pictured: A monkey being restrained ahead of tests
The tests are carried out to determine safety margins for use of the drug, how compounds move around the body and what affect this has on organs
The unprecedented footage was captured by a former lab worker who said he could no longer remain silent about the “immense distress” the primates and other species endure. Speaking to The Mail on Sunday, he described being “haunted” by the shrieks and whimpers that echoed through the facilities for up to two years during some trials. “My conscience wouldn’t let me just quit and walk away,” he said. “I felt if I was able to provide a window into this world that had been hidden from public view, perhaps it would change.”
The tests, conducted at Home Office-regulated sites contracted by major pharmaceutical companies, are legally required to assess safety margins, how compounds move through the body, and their effects on organs before any drug can advance to human clinical trials. Long-tailed macaques are used for weight-loss and liver-disease medications. Beagles undergo similar gavage procedures for anti-inflammation drugs. In separate inhalation tests, masks are strapped to the faces of both monkeys and beagles; the primates are first secured in vices around their necks and waists. Mini-pigs have eight cuts made on their backs for ulcer and skin-infection treatments, with gel applied daily. Pregnant rabbits are dosed to evaluate effects on embryo survival and development. Intravenous injections and infusions are also performed on restrained animals.
Every procedure is carried out within the law. Yet the whistleblower, who worked at both sites, said the suffering he witnessed was normalised by a workplace culture that framed the work as “something positive for the world.” Signs on the walls reinforced the message, but he quickly stopped “drinking the Kool-Aid.” Lab staff sometimes played music to distract themselves, yet the animals’ distress remained impossible to ignore. “The primates would struggle, cry out and scream to avoid the tube from being forced into their mouths,” he recalled. “I’ll never forget the loud squealing of mini pigs.” At the end of every trial, surviving animals are euthanised and dissected for further analysis. “Part of you knew that it meant an end to their suffering,” the former worker said, “but it still felt like a final violation.”
The scope of the testing extends far beyond experimental weight-loss injections. Beagles, pigs, rabbits and other species are used to evaluate everyday products including headache tablets, cholesterol drugs, reflux medications, antihistamines, antibiotics and antidepressants. Psychoactive and psychedelic compounds, including cannabis extracts and an ingredient found in ecstasy, have also been tested on beagles for potential psychiatric treatments. All animals that survive the dosing regimes are killed once the studies conclude.
Mini pigs are used to test medication for ulcers and skin infections by using treatments where eight cuts are taken from the back of the struggling animalF
In other tests, masks are strapped to the faces of beagles and monkeys and the trial substance inhaled by the animals
Campaigners have reacted with outrage. Lyn White, director of Animals International, who was contacted by the whistleblower, described the footage as evidence of “prolonged and cumulative” suffering: weeks or months of repeated dosing, restraint and confinement. “These animal tests, despite being conducted in the name of public safety, have been hidden from public view,” she said. Labour MP Irene Campbell, chair of the All-Party Parliamentary Group on Phasing Out Animal Experiments in Medical Research, called the evidence “terrible suffering” that demands “bold and immediate action to accelerate the phase-out of animal experiments” in favour of innovative, human-specific methods.
Yet defenders of the current system argue that such extreme cases are rare and that the tests remain essential. Chris Magee of Understanding Animal Research noted that “extreme suffering” is “extremely rare” and that the footage appears to highlight “the rarest and most severe experiments required or permitted by law.” He pointed out that it is already illegal to use an animal if a non-animal alternative exists, and that dogs and primates are the least-used species. Routine animal testing was introduced in the UK in 1968 after tragedies such as thalidomide demonstrated the dangers of insufficient safety data. Under current rules, primate testing is restricted to research aimed at preventing or treating “debilitating or potentially life-threatening clinical conditions in man,” and any procedure likely to cause pain must use anaesthesia or painkillers unless it would invalidate the results.
Animal testing for regulatory purposes has already fallen 43 per cent in the past decade. Magee stressed that full replacement is not yet possible because alternatives such as cell cultures or organs-on-chips cannot replicate the complexity of a whole living system – including absorption, distribution, metabolism and potential environmental impact of drugs after excretion. Post-mortem examinations remain the only way to understand disease development fully, he added. Many of the medicines that reach chemists – cancer treatments and statins among them – are life-saving precisely because of these tests.
The debate has gained fresh urgency following last month’s announcement by the US Food and Drug Administration. The FDA issued new guidance encouraging drug developers to explore alternatives to animal testing, citing “growing scientific recognition that animals do not provide adequate models of human health and disease.” It noted that over 90 per cent of drugs safe and effective in animals fail in human trials, often due to safety or efficacy issues, and that some compounds lethal to humans had appeared safe in animal models. The regulator is promoting computer modelling, artificial intelligence, lab-grown human organoids and organ-on-a-chip systems as more reliable, efficient and ethical predictors of human reactions.
Pro-testing groups counter that the FDA’s 90-per-cent failure statistic is a misconception, claiming animal data aligns with human data in roughly 90 per cent of cases when properly evaluated in clinical trials. They maintain that the footage, while disturbing, does not represent standard practice and that the public benefits from medicines whose safety has been established through these rigorous, legally mandated processes.
The whistleblower knew the risks he took in secretly filming the procedures. “I had no idea what toxicity testing regulations required until I applied for the job,” he said. “I wouldn’t have taken the risks I did if I hadn’t believed that the sole reason this continued was because the public didn’t know.” His decision to release the material has thrust the ethical cost of drug development into the spotlight – particularly for the weight-loss medications now marketed directly to consumers chasing slimmer bodies.
Whether the disturbing images will accelerate Britain’s pledged phase-out of animal testing remains to be seen. For now, they serve as a stark reminder that behind every new pill, injection or tablet promising better health lies a hidden world of restraint, dosing and sacrifice – one that, until this week, had remained largely invisible to the very people it is intended to protect.