Clinical Trials

What are clinical trials and why do we need them?

Clinical trials are research studies involving people. They test whether particular treatments are safe and how well they work. (‘Trial’ in this sense means testing something, and has nothing to do with legal trials or court cases).
We need to know: 
  • Does a treatment work?
  • Does it work better than other treatments?
  • Does it have any side effects?
Clinical trials are designed to answer these questions and improve health and quality of life for patients. Until well-designed trials have been carried out, we simply do not have enough evidence to know if a treatment is both effective and safe. Without trials, there is a risk that people will be given treatments which do not work and which may even be harmful.
Experimenting and testing have long been a part of medicine, and there are many different kinds of trial. (See below for an explanation of Phase 1, Phase 2, Phase 3 and randomised controlled trials). It is only quite recently that randomised clinical trials (RCTs) have been generally recognised as the best way to compare different approaches to preventing and treating illness. They can be used to compare drugs, but also to compare other types of treatment, across a range of conditions. (See also ‘Different types of trial’).
It may come as a surprise to many people that sometimes doctors don’t ‘know’ which treatment is the best. When doctors make decisions about how to treat a particular illness or condition, they use their medical knowledge, based on the textbooks they have read, the results they have observed in previous patients, similar observations by their colleagues, what they have heard at conferences and what they have read in medical journals. RCTs provide a different kind of knowledge, based on statistics; this type of knowledge sometimes shows that what doctors had ‘known’ in the everyday sense was wrong.
Phase 1 and Phase 2 trials
Many clinical trials (especially for new drugs) are carried out in a number of stages, or phases. When a new treatment is first developed, such as a new cancer drug, it will be tried first in a few people to get an idea how safe it is. They may be healthy volunteers, who are given a compensation payment for taking part, or they may be people who are ill, perhaps people who have already tried all the usual treatments. This is called a Phase 1 trial. At this stage, the treatment is usually given to all those taking part, and it is not being compared against some other treatment (see below).
By the time a drug reaches Phase 2, researchers will know more about it. In Phase 2 the aim is to test the new drug in a larger group of people to better measure safety and side effects and see if there are signs of positive effects in patients. Phase 2 trials may or may not involve comparison with another treatment (see below).
In Phase 2 trials we can start to get some idea of whether a treatment works for some people, and what kind of side effects they experience. But at this stage the numbers of people included are still too small to give us firm evidence about its effects and that any observed change is not just happening by chance. This is why Phase 3 trials are needed.
Phase 3, randomised clinical trials
Phase 3 trials are usually large, and may include hundreds or even thousands of patients. They often compare the effects of newer drugs or treatments with standard treatments if there are any. They provide a better test of whether new treatments work better than existing treatments, and firmer evidence about how common and serious any side effects are.
Almost all Phase 3 trials are randomised clinical trials (RCTs). In an RCT, one group of people, the experimental group, is given the new treatment. The other group, called the control group, is given the standard treatment. If no standard treatment exists, the control group may not be given any specific treatment or may be given a placebo. Some trials may compare more than two groups.
A placebo is a treatment, with no active ingredient, which is designed to appear very like the treatment being tested. By comparing people’s responses to the placebo and to the treatment being tested, researchers can tell whether the treatment is having any real benefit, rather than patients simply feeling better because ‘something is being done’.
There are several ways in which the results of trials can be made as reliable and accurate as possible. One of these is to make the trial a ‘blind trial’. In a blind trial the participants are not told which group they are in. This is because if they knew which treatment they were getting it might influence how they felt or reported their symptoms. Some trials are double-blind, which means that neither participants nor the doctors and others treating them know which people are getting which treatments. This also avoids the doctors’ hopes and expectations influencing the results of the trial
Here Wendy describes a typical RCT design comparing standard treatment for bowel cancer with an extra chemotherapy drug.
(Sometimes you may hear the experimental group called the ‘trial group’ or ‘intervention group’. This can be confusing, as all the groups, including the control group, are part of the trial, and people in the control group may also be given an intervention, in the form of the standard treatment).

To make sure that each group contains a similar mix of people, many trials are ‘randomised’. This means that people are allocated at random to one of the groups in the trial, often by using a computer programme. When people are randomised they have an equal chance of being in either of the trial groups. Random allocation helps ensure we are comparing two very similar groups of patients, so if one group does better than another, it is very likely to be because the treatments being compared have different effects, and not because of differences between the people in the groups. (See also ‘Feelings about being allocated (randomised) to a treatment group’ and ‘Feelings about being in a placebo-controlled trial’).
Many people have heard of clinical trials of new drug treatments, especially in the field of cancer. But clinical trials can also be used to test and compare all sorts of different types of treatments across a range of conditions, including surgery, physiotherapy and rehabilitation programmes, screening, prevention (such as vaccines), complementary therapies, radiotherapy and chemotherapy. They can evaluate talking therapies such as cognitive behavioural therapy for mental health problems and behaviour change programmes, and they can be used to assess the value of particular tests for screening or diagnosis. Trials can also compare different ways of giving people health information. (See ‘Different types of trial’ for examples).
Clinical trials are designed by doctors, scientists and others, and increasingly together with patients. The first step is to decide which questions need answering, and then to look carefully at the results of any trials that have already been done and any other research evidence (a systematic review). Then doctors, nurses, patients and researchers work together with statisticians and trial managers to design the trial. This is written down in the trial protocol. All trial protocols in the UK have to be approved by a research ethics committee which checks that the trial is ethical. In particular they should check that the questions being addressed in the trial have not already been answered, and that people are asked to take part in an appropriate way, with clear information to help them decide whether to take part.
Lester, whose son Ellis died of Creutzfeldt-Jakob Disease (CJD), was asked to help chair the committee for a trial of treatments for CJD. Here he explains the process of designing and approving the trial, and the important role lay representatives can play.
For further information, see our Resources section.

Last reviewed September 2018.
Last updated June 2013


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