Skip to main content

Experimentation is an essential part of scientific medicine. But in medicine, the subjects of experiments are often people.

Doctors have always conducted investigations and experiments in order to understand the body in sickness and health, and to test the effectiveness of treatments. Medical laboratories carry out experimental research into new techniques and treatments, but at some point developments intended for use on patients have to be tested on people. 

Experimenting with the living—animals and humans—is complex and sometimes dangerous. In their efforts to discover more about diseases and find effective treatments, doctors and researchers have put vulnerable and powerless patients at risk. 

The modern clinical trial—an experiment in which people are the test subjects—has developed over time not only to ensure the optimal conditions to produce valid, scientific results but also to safeguard the rights and well-being of participants.

Clinical trials

In the 11th century CE, the Islamic physician Ibn Sina put forward rules for testing the effect of drugs on patients. One key criterion was that:

The effect of the drug should be the same in all cases or, at least, in most. If that is not the case, the effect is then accidental, because things that occur naturally are always or mostly consistent.

Ibn Sina

This remains the essential criterion for any treatment—that it has the same effect on most patients in similar conditions. But testing a drug on one person does not tell you very much. Their response may not be typical, side effects may be the result of an allergy, or their recovery may be due to some external factor. 

Large-scale drug trials and medical investigations with many patients were only possible once hospitals became places of research in the 19th century. Hospitals provided opportunities to observe and compare large numbers of patients with the same disease in the same environment. 

Today new medical treatments and drugs have to undergo several stages of testing before they reach the final stage of being tested on people. Usually a therapy is tested on animals before clinical trials are permitted. 

Participants in clinical trials are carefully selected in order to limit the number of variable factors that might affect the results. For example, only patients at the same stage of a particular condition may be selected in order to see if a new therapy is effective in treating the condition at that stage.

In order to run a clinical trial on patients, researchers have to go through a rigorous procedure that includes registering the trial with the authorities and presenting their proposal to an ethics committee, who will decide it the trial is valid and that there are safeguards in place to ensure that participants understand what will happen to them.

Randomised clinical trials

In randomised trials, the test subjects are divided into at least two different treatment groups. Participants are assigned to a group at random. 

One group is usually given the standard treatment for their condition. They are the control group.  People in the other group (or groups) will have the treatment or procedure that is being tested. A randomised trial that has a control group is called a randomised controlled trial (RCT).

If there is no standard treatment, then people in the control group may be given a dummy treatment, called a placebo. A placebo is a treatment with no medical effects. It allows researchers to take into account the psychological influence of experiencing treatment, regardless of what is in the treatment. 

A blind trial is a trial where the people taking part don't know which treatment they are getting. A double blind trial is a trial where neither the researchers nor the patients know what they are getting. The identity of patients in each group is kept secret until the end of the trial. 

Protecting participants in clinical trials

In the past, participants in medical experiments have been susceptible to abuse. Some groups of people had no choice in whether or not they participated. For centuries, executed criminals had their bodies subject to dissection as part of their sentence. Prisoners were used to test the new cholera vaccine in colonial India. 

And troops heading to the South African War (1899–1902) were offered a new typhoid vaccine before it was fully tested and the side-effects were understood and eliminated—one reason why take-up of the vaccine was so low and thousands died from the disease.

Patients in psychiatric hospitals have been particularly vulnerable to being treated without their consent and without understanding their treatment. In the first half of the 20th century, psychiatrists desperate to find effective treatments for conditions such as schizophrenia tested experimental convulsive shock therapies on their patients, when they themselves had little knowledge of the effects.

After the trials of Nazi doctors who had conducted human experiments during the Second World War, the Nuremberg Code was devised, offering a set of research ethics for human experimentation. The ten points in the code included the need for informed consent and the absence of coercion.

Most countries now have regulatory boards for clinical trials that insist on informed consent before people can participate in clinical trials. 

Animal experiments

Animals have been used for dissections and medical experiments since antiquity. For centuries, human dissection was severely restricted and physicians and surgeons relied on animal dissection to learn about anatomy. 

The Roman physician Galen dissected pigs and monkeys to develop his knowledge of anatomy, although he was aware that the human body was different in many ways.

Most researchers saw nothing wrong with experimenting on animals. Religious authorities said that animals had no souls and they were under the dominion of mankind, along with the rest of the natural world. The 17th-century philosopher and researcher René Descartes (1596-1650) claimed that animals did not feel pain.

The number of experiments on animals increased in the 19th century with the rise of life sciences such as experimental physiology. The French physiologist Claude Bernard used animals in his research and drew criticism for it from opponents, including his own wife and daughters.

As scientific animal experimentation grew, so did the anti-vivisection movement. In 1875 the activist Frances Power Cobbe founded the Society for the Protection of Animals. The protests of the early animal rights movement led to the Cruelty to Animals Act of 1876, which regulated animal experimentation.

Louis Pasteur used rabbits to develop a vaccine for rabies and was the target of anti-vivisection protests.

Engraving of three men standing around a lab bench with a dead rabbit Wellcome Collection (CC BY) Image source
Pasteur (left) watching a colleague trephining a chloroformed rabbit during his research on rabies vaccination, 1885.

Modern medical research still relies on animals. As well as medical research, testing on animals, primarily rats and mice, is used to assess the safety or effectiveness of products such as drugs, chemicals and cosmetics. But medical researchers are increasingly aware of animal welfare and continue to seek scientific alternatives to animal testing. 

Where the ability to replace animal experiments with alternatives such as tissue cultures, microorganisms or computer models is limited, researchers have tried to reduce the amount of animal testing needed. This is because, apart form the ethical concerns, animal experiments are expensive and (as with all experiments on living organisms) highly complicated.

Both scientific research organisations and animal rights groups promote the use and development of methods of scientific testing that don’t use animals, such as:


Occasionally medical researchers decide to test a new idea or treatment on the most convenient test subject around—themselves. They might do this because the weight of medical opinion is resistant to their idea and they can’t get funding or support to test it any other way. 

Or they might simply have wanted to prove their theory before sharing it with others. Whatever their reasons, self-experimentation has contributed some valuable treatments and techniques to medicine—but it has also gone very wrong.

Suggestions for further research