Monkeys play a crucial role in understanding and combating infectious diseases that affect humans. Their immune systems are similar to ours, allowing them to respond to infections and vaccines in comparable ways. All leading COVID-19 vaccines (Moderna, Oxford/AstraZeneca, Pfizer/BioNTech and Johnson & Johnson) were tested for safety and efficacy in rhesus macaque monkeys before human trials. During the COVID-19 pandemic, monkey studies were essential to confirm that vaccine candidates could protect against the virus and were safe to use in people. 
Likewise, monkeys have been key in developing vaccines or treatments for other deadly outbreaks: for example, experimental monoclonal antibody therapies for Ebola achieved 100% survival in infected monkeys, providing confidence to use them in patients. 

Monkeys are also susceptible to simian immunodeficiency virus (SIV), a close relative of HIV, which allowed researchers to develop the combination antiretroviral therapies (ART) that have transformed HIV/AIDS from a fatal illness to a manageable condition. These are cases where no other animal model reliably replicates human disease. 

As a recent U.S. National Academies expert panel emphasised, research with monkeys “is critical to [our] ability to respond adequately to public health emergencies and carry out high-impact biomedical research”. Their report warned that without enough monkeys for research, our capacity to develop life-saving vaccines and treatments for diseases like COVID-19, Ebola, polio or measles would be severely compromised.

Monkeys’ complex brains make them indispensable for studying the nervous system and diseases of the brain. A small number of monkeys are used in research on neurodegenerative diseases like Parkinson’s and Alzheimer’s, where rodent models often fail to mimic key aspects of the human condition. 
For example, monkey experiments were fundamental in developing Parkinson’s disease treatments. Therapies like levodopa (to replace dopamine), deep brain stimulation (electrical implants to reduce tremors), and gene therapy for Parkinson’s were refined through studies in monkey models. In 2020, French scientists created a special oxygen-free dopamine formulation and infused it into monkeys with Parkinson’s, significantly improving their movement symptoms without toxic side effects, leading to potentially better treatments. 

In 2020, a team at the Netherlands Institute for Neuroscience demonstrated a high-resolution brain implant in monkeys that could partially restore vision. Tiny electrode arrays in the visual cortex of two sighted monkeys induced artificial visual patterns, proving the concept of a visual prosthesis. Dr. Xing Chen, the study’s lead researcher, explained that such technology could restore low vision in blind people with intact visual cortices. This EU-funded advance brings us closer to neuroprosthetic devices for blindness. Monkeys’ complex cognitive tasks make them crucial for research on memory, decision-making and psychiatric illnesses. 

Monkeys’ brain chemistry and behaviour in response to addictive drugs mirror humans, confirming how substances like cocaine reinforce dependency. They’ve also contributed to mental health research, with the first biochemical theory of depression being informed by monkey observations, paving the way for antidepressant medications. 

Research with monkeys has also been central to the development of neuroethology — a field that explores how brain circuits generate natural behaviour in real-world contexts. Neuroethology brings together neuroscience, behaviour and evolution to understand how perception, decision-making and action are linked in complex brains. Because monkeys share advanced sensory systems, social behaviours, and brain organisation with humans, studies in non-human primates have been particularly important for linking detailed brain activity to cognition and behaviour — insights directly relevant to understanding human neurological and psychiatric disorders.

Today, neuroscience studies using monkeys underpin development of brain–machine interfaces to help paralysed patients, new neurotherapeutics for disorders like epilepsy, and even advances in AI (by modeling primate vision and decision processes).

Scientists studying monkeys and apes are gaining insights into human mental health. For instance, researchers observed wild chimpanzees in Guinea drinking fermented palm sap and eating alcoholic fruits, consuming measurable ethanol without intoxication. This supports the “drunken monkey hypothesis”, suggesting early primates evolved to seek fermentation smells as cues for ripe, energy-rich fruit, potentially shaping humans’ attraction to alcohol. 

Studies of macaques and marmosets have shown that monkeys can display depression- and anxiety-like symptoms, such as social withdrawal, disturbed sleep and loss of interest in food or play, similar to humans. These behavioural patterns help researchers identify brain circuits and hormones involved in mood regulation. 

Other research has revealed that non-human primates can also model human addiction and stress-coping behaviours. More recent behavioural studies have focused on how social relationships protect primates from stress. For instance, a study in 2026 found that same-sex sexual behaviour in over 50 primate species helps strengthen bonds and reduce social tension, highlighting how social connection can act as a natural buffer against stress.
Together, these discoveries show that the foundations of human emotional health — from addiction and anxiety to stress relief and social bonding — are deeply rooted in our primate past.

Before new medicines reach human clinical trials, they must undergo rigorous animal testing for safety and effectiveness. Monkeys are often used in advanced biotechnologies, especially when a drug is highly specific to human biology and does not work in typical lab animals like dogs or pigs. This is increasingly common with modern biopharmaceuticals, such as monoclonal antibody treatments that target human proteins. In these cases, monkey studies are crucial to evaluate dosage, detect side effects and ensure the therapy interacts correctly with the human body. Gene therapies, which alter a patient’s genes to cure disease, have also relied on monkeys for testing.
A striking example is the development of base editing, an advanced form of CRISPR gene editing that can “fix” single DNA mutations without cutting the DNA strand. In 2023, researchers reported using a new prime editing technique(related to gene editing) to correct genetic mutations in the livers of monkeys, as a proof-of-concept for treating metabolic diseases, paving the way for human trials. As Prime Medicine’s chief scientist noted, demonstrating a working, safe delivery system in monkeys was a “big celebration” for the future of genetic therapies. 

Monkeys are used to study drug processing in the body (toxicokinetics), tracking absorption, distribution, metabolism and excretion. Their human-like processes help predict dosing and identify toxic by-products. As biomedical innovation accelerates, the need for monkey models in safety testing grows. In 2019, five of the 29 new medicines approved by the U.S. FDA were complex “biological” drugs, all requiring monkey studies to evaluate toxicity. The European Medicines Agency and other regulators agree that certain studies, like those on fertility or immune therapies, must use NHPs if no other species is suitable. However, these studies are strictly monitored and only conducted after exhaustive efforts to find alternatives. 

A lesser-known area where monkeys have been invaluable is in studies of human reproduction, pregnancy and development. Because monkeys have reproductive systems and hormonal cycles very similar to ours, they have contributed to several medical advances in this field. Research with rhesus monkeys in the 20th century was critical in developing in vitro fertilisation (IVF) techniques, which have since allowed millions of people to conceive children. Monkeys were also at the heart of the discovery of the Rhesus factor in blood – the Rh factor, named after rhesus macaques, is the blood antigen that can cause complications in human pregnancies (and blood transplants). Some reproductive studies continue with monkeys to answer questions that can’t be studied in humans. 

For example, in 2022 scientists created the first detailed atlas of egg cells in the primate ovary, tracking the lifetime supply of eggs in monkeys. This kind of research improves our understanding of female fertility and ovarian ageing – knowledge that could inform new treatments for infertility or menopause-related conditions. 
Monkeys have been used to improve care for newborn infants. Studies in baboons (a type of NHP) helped researchers develop better strategies for ventilating premature infants’ fragile lungs, reducing lung injury in preterm newborns. Scientists have also used monkeys to study how infections during pregnancy might trigger pre-term birth, an important finding since such infections are difficult and unethical to study in pregnant women. By observing how maternal infections affected pregnancy outcomes in monkeys, researchers identified inflammatory pathways that could be targets for preventing premature labour. 

Monkeys have contributed to numerous medical breakthroughs in cardiovascular research. They naturally develop heart artery disease on high-fat diets, making them ideal for testing cholesterol-lowering interventions and understanding heart failure progression. Drugs that aid heart muscle repair after a heart attack showed promising results in pigtailed macaques. In immunology, monkeys have been crucial in developing drugs that prevent organ transplant rejection. The first successful anti-rejection medications, like ciclosporin, were optimised in monkey transplant models that closely predicted human immune responses.
Monkeys are occasionally used in studies of illnesses like cancer when a primate-specific model is needed. While rodent models cover many cancers, some therapies, especially immunotherapies, rely on primate tests. For instance, the breast cancer drug Herceptin was found to pass into breast milk based on monkey studies, leading to advice that nursing mothers avoid it. In immunology, monkeys have been central to developing drugs that prevent organ transplant rejection.
Monkeys also helped confirm the safety of the oral polio vaccine decades ago, but transgenic mice engineered with a human poliovirus receptor have now replaced monkeys in routine polio vaccine batch testing.