Skip to main content

Clinical trials and medical experiments

Published: 30 July 2019

Experimentation is an essential part of scientific medicine. 

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 1030s, the 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. 

Today new medical devices and drugs have to undergo several stages of testing before they reach the final stage of being tested on people. Drug testing and regulation was tightened in the mid-1960s following the impact of thalidomide worldwide. 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 people, 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. 

What is informed consent?

Legally and ethically, participants in a clinical trial need to have adequate information to allow for an informed decision about participation in a trial. This includes what tests are involved what the risks and benefits may be, how much of your time it will take and what will happen to any of your samples after the trial. 

The modern definition of informed consent came out of the Nuremberg trials, a series of legal trials between 1945 and 1947 to prosecute surviving German war criminals after the Second World War. 

People were shocked by the horrific things done by doctors in the name of medical research and the Nuremberg Code was developed as a result. It is the basis for all rules regarding human experiments, including the requirement for informed consent.

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

Before the Nuremburg Code, people in charge of human experiments did not have to tell their patients what they were doing. Some groups of people had no choice in whether or not they participated. 

British troops heading to the South African War (1899–1902) were offered a new typhoid vaccine before it was fully tested and the side-effects understood and eliminated. These side effects were one reason why take-up of the vaccine was so low.  Alongside volunteers, some prisoners were used to test a new cholera vaccine in India in 1897. 

Throughout the 1900s, psychiatrists who wanted to find effective treatments for conditions such as schizophrenia tested experimental convulsive shock therapies on their patients. Researchers had little knowledge of the effects—and patients were not always asked for their consent.


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.

Animal experiments

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

The Roman physician Galen dissected pigs and monkeys to develop his knowledge anatomy. Although he was restricted by law to dissecting animals, the three years he spent from 158 CE as physician to the gladiators of his home city of Pergamon were a formative period in his life in medicine. The traumatic injuries he regularly encountered gave Galen the perfect opportunity to extend his practical medical knowledge of the human body.

Discussions about whether to experiment on animals has always been part of the debate.
Some 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 1600s philosopher and researcher René Descartes (1596-1650) claimed that animals did not feel pain.

The number of experiments on animals increased in the 1800s 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.

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

Pasteur (left) watching a colleague trephining a chloroformed rabbit during his research on rabies vaccination, 1885.

As scientific experimentation on living animals, known as vivisection, 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 in England, Wales and Ireland.

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. 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 from 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:

Suggestions for further research


  • A Harrington (ed.), The Placebo Effect: An Interdisciplinary Exploration, 1997
  • J S Hawkins and E J.Emanuel (eds.), Exploitation and Developing Countries: The Ethics of Clinical Research, 2008