Why Intentionally Stressing Animals Is Not Good Science

Following discussions with PETA entities, 15 companies and three universities, including King’s College London, have declared that they do not intend to use the forced swim test (FST) in the future. Despite this, some institutions are still carrying out or refusing to ban the cruel test. Here, we explain why the FST must be ended, for the sake of animals, scientific progress, and human health, as potential new treatments are being delayed by these meaningless tests.

What is the forced swim test?

In the FST, experimenters place mice, rats, or other small animals into inescapable beakers filled with water. Terrified, they swim in search of an escape, and experimenters record how long it takes before they stop swimming and float on the surface.

Experimenters absurdly claim that this test tells us about human mental health conditions, such as those caused by stress – but the science does not hold water and distressing animals does not help humans.

How is the test used?

For decades, floating behaviour in the FST was considered indicative of the feeling of despair experienced by humans with clinical depression or other mental health conditions. However, scientists now realise that floating is not a sign of despair but may be indicative of learning – a way to conserve energy and adapt to a new environment.

Its use in depression research has been widely criticised. In 2021, a group of scientists, comprising individuals from the UK Medicines and Healthcare products Regulatory Agency, published a scientific paper on the initiative of the Home Office’s Animals in Science Regulation Unit (which regulates experiments on animals) calling for researchers to seek alternatives to the FST for studying antidepressant drugs. The paper recognises that the test is a poor model of human depression and could rule out the discovery of effective new drugs for humans.

Hasn’t the test played an important role in the development of antidepressant drugs?

Quite simply, no. Also in 2021, PETA US neuroscientist Dr Emily Trunnell, along with psychologist Dr Constança Carvalho, published a paper in the esteemed journal Drug Discovery Today. The paper examines the use of the forced swim test by the 15 most profitable pharmaceutical companies in the world, showing its poor accuracy for identifying antidepressants for human use. Of the 109 compounds identified, the test appeared to predict antidepressant efficacy for only three, but none of them are currently approved to treat any type of depression.

What else is the test used for?

The FST is also used in attempts to study other stress-related mental health conditions in humans. But animals used in this archaic test experience acute stress, unlike humans suffering from stress-related mental health symptoms.

Human stressors that contribute to poor mental health are typically chronic in nature. They include psychological symptoms that are not measurable in other animals, such as flashbacks, emotional numbness, and detachment.

Living far away from their normal habitats and being unable to do anything that is natural and important to them while every aspect of their lives is controlled by experimenters, mice and rats in laboratories endure psychological and physical stress every day from spending their lives in a cage.

The conditions the animals are kept in undermine the integrity of the data and the relevance of the FST for human stress research.

What is the effect of the test on animals?

Because the FST is stressful for animals, it has also been criticised for its effect on their welfare. Consider how exhausting and distressing this test must be for rats and mice. Imagine spending your life trapped in a cage before being forced to take part in an experiment meant to cause you stress, only to be killed afterwards.

When the animals have served their purpose, experimenters may kill them by giving them an overdose of anaesthetic, breaking their necks, gassing them, or striking them on the head. Their bodies are then thrown away like disposable laboratory equipment.

But isn’t testing on animals important for medical research?

Trying to understand the fundamental human biology underlying stress and anxiety by forcing rats to swim in a beaker of water is doing a disservice to those suffering with mental health disorders. Stress-related mental health conditions, such as depression, are some of the most common and debilitating conditions in the world, making it vital that scientific research achieve translatable results that are relevant for human clinical practice.

Institutions could stop using the test right away with no detriment to mental health research. There are plenty of human-relevant approaches that do not involve stressing animals. Researchers are already using three-dimensional models of the brain grown from human stem cells to gain insights into human mental health conditions.

Join us in calling on the University of Bristol to ban the forced swim test: