What is a clinical trial?

What is a clinical trial?
Clinical trials are medical research studies that involve people. New drugs are first studied in a laboratory, and those that look promising go on to be carefully studied in people through clinical trials

The aim of a clinical trial is to test new drugs to see how well they work in helping people feel better, or in helping a disease to improve or stop getting worse. Clinical trials also test whether new drugs are safe and if they have any side effects. Without clinical trials, there would not be enough proof that a new treatment works and is safe. All current drugs that are available to you, either at the hospital or from the pharmacy, have been carefully tested through clinical trials. There is evidence that shows how well these drugs work and if there might be any side effects. This information is vital to help doctors understand which treatments are the most suitable for their patients, and for official groups (called the regulatory authorities) in each country or region to decide whether to approve a drug for use.

Although the aim of a clinical trial is to find new, better treatments, not all clinical trials result in a better treatment. A new drug may not work as well as drugs that are currently used, or may have worse side effects. However, even this information is very useful to the trial investigators, and goes on to help patients in the future.

Watch our video, “What is a Clinical Research Study?”, to learn more about clinical trials.

Different types of trials
Clinical trials are divided into different phases of testing: phases 1, 2, 3, and 4, which are often also written as phases I, II, III, and IV.

Phase 1
At first, a new drug is tested in just a small number of people. These can be either patients who have tried every other type of treatment for their condition or healthy volunteers. This is called a phase 1 trial. All people in a phase 1 trial receive the drug being tested, usually in small doses, without comparing it to another treatment.

This type of trial helps to find out how much of the drug is safe to give, if there are any side effects, if the treatment can improve the disease (for example, shrink a tumour in a cancer patient) and to see how the body copes with the drug.

Phase 2
When a drug reaches phase 2, more is known about how it affects the body. In this type of trial, the drug is given to a larger number of patients, up to 100 or so. The new drug may or may not be compared to a treatment that is currently given to patients.

The aim of a phase 2 trial is to see if the new drug works well enough to be tested in much larger groups of patients in a phase 3 trial (see below). It will look at how well the new treatment works in a disease, how to manage any side effects and how much of the drug is safe to give to patients. At this stage, the drug has still not been tested in enough people to know for sure that any positive changes are caused by the drug and not just by chance.

Phase 3
Phase 3 clinical trials are usually much larger and can include thousands of patients. Here, the new drug is often compared to the standard treatment to see whether the new drug has any benefits over current drugs. This also helps to obtain firmer proof of what the drug side effects are likely to be for patients.

If a drug can show an improvement over the standard treatment in a phase 3 clinical trial and is safe to use, it is likely to be approved by regulatory authorities so that it may become the new standard treatment for patients with that disease.

Phase 4 (also known as post-marketing surveillance trials)
Phase 4 trials take place after the medicine has been given regulatory approval (also known as ‘market authorisation’). Phase 4 trials are done to provide more information about how well the drug works and how safe it is in a larger number of patients. A phase 4 trial might also look at the drug in patients with particular characteristics, or compare or combine the new drug with other available treatments. Phase 4 trials also look at patients who take the drug for a longer period of time.

How do we know if a clinical trial is fair and balanced?
For a drug to be approved, the supporting clinical trials must be designed in a way that is fair, in order to give reliable and accurate results. The main ways that are used to make clinical trials fair and balanced are:

Randomisation – One way that a trial is made fair is to ‘randomise’ patients. This means that participants are split into two (or sometimes more) groups randomly (by chance, like flipping a coin). In some cases, one group will be given the new drug and the other group will be given the standard treatment, or a placebo if no standard treatment exists. In other cases, there might be several groups being given different doses of the new drug alongside a group being given the standard treatment or placebo. The randomised groups are balanced based on various things such as age, gender (male/female) and other patient features. This means that the different treatments can be compared across groups of similar people. This is how any differences between the effects of the treatments can be seen by the researchers.

Placebo – A placebo is a treatment with no ‘active ingredient’ or real drug. It will usually look and feel very much like the real treatment so that the researchers can compare whether the trial drug is having a real effect. It is important to remember that there is no guarantee that the new trial drug will be better than the standard treatment.


Blinding – Another way that trials are made to be as accurate as possible is to make the trial a ‘blind trial’. This means that patients are not told whether they are being given the drug that is being tested, or not. If the trial investigators/doctors also do not know (until the very end of the trial), which patients are being given which treatment, this is known as a ‘double-blind study’, and helps to prevent bias and expectations from the investigators.

Who’s involved in a clinical trial?

Patients (or sometimes healthy volunteers) – The most important people who are involved in a clinical trial are the patients or healthy volunteers. Without patients and volunteers, trials could not be carried out and new drugs could not be developed. The decision to join a clinical trial is made by the patient or volunteer, after talking to their medical team. Patients and volunteers are free to decide to enter a trial, and may leave at any time.

Specialist – It is most likely that you will have a specialist looking after you whilst you are in a clinical trial, for example, in a cancer trial, this would be your oncologist. This person will be checking your health and your condition very closely during the trial and will look carefully at all of your test results along the way. They may also speak to research staff or people from the drug company to ask questions or raise any concerns.

Clinic nurses – Your specialist is likely to be supported by clinic nurses who will carry out some of the tests and look after you whilst you are having treatment in hospital.

Other people involved in your care – You may meet other hospital staff who are involved in your care whilst you are in the trial, for example, radiographers who will carry out some of the scans you might have. There will be other people you might not even meet, for example, the people who carry out some of the tests in laboratories at the hospital or elsewhere.

Research staff from a CRO A CRO is a Clinical Research Organisation, which is an independent company who may partner with the pharmaceutical company to help to set up and run the trial. A CRO specialises in running clinical trials, and so can offer in-depth knowledge, as well as being completely independent and objective. You may meet research staff from a CRO if you take part in a trial.

General Practitioner (GP) – Your GP will be aware that you are in a clinical trial, but is unlikely to know all of the details.

Pharmaceutical company – There are many researchers and medical specialists from the pharmaceutical company who are developing the new drug, who will closely check all of the information and results they are given by hospitals and doctors.

What happens before, during and after a clinical trial?

Before taking part in a clinical trial, you will need to sign a form to say that you give your ‘informed consent’ to take part. To do this, your doctor should explain to you what the trial is aiming to show, any possible benefits and risks involved, and how taking part in the trial will affect you. Once you understand the trial, you can decide whether you would like to take part.

To join a particular trial you must also meet certain criteria, such as being of a particular age range or gender (male/female), or having a specific type of disease (for example, in a cancer trial this might be the type of tumour you have, where the tumour is located, whether the cancer has spread, etc.). This is likely to mean that after agreeing to take part you will need to have a range of tests, such as blood tests, scans or biopsies, before you can be given any treatment as part of the trial. Your doctor will be able to tell you what tests will be needed for a trial that you are interested in.

How and where you take your treatment will depend on the clinical trial. If the treatment is an oral pill or an injection, you may be able to take the treatment at home. In some cases, you may have to travel to a hospital or clinic to receive your treatment as an infusion where the drug is given into your vein. Taking time off work in order to travel to and from appointments may be difficult for some people, so bear this in mind when you are deciding whether to join a trial. Think about whether there might be anyone close to you who may be able to support you with travel. Many trials will provide compensation for travel to trial centres, but it is a good idea to think about all of the ways that taking time away from work to attend appointments will affect you or a carer.

During the clinical trial, once you have started to be given your treatment, you may need to have regular tests to help researchers find out how well the treatment is working and if there are any side effects. You may be asked about any new symptoms you are having or asked to fill in surveys about how you feel or how well you are able to carry out your day-to-day activities. These extra tests may mean that you end up visiting your GP or clinic more often than you would normally.

All this extra attention might be of value to you, as changes in your health may be picked up and addressed much more quickly than if you were not in a trial. You may also find that more contact with your healthcare team means that you have more chances to ask questions and find out more about your condition or the treatment.

If you are being given a new treatment as part of the clinical trial, it may not always be possible for you to continue this treatment once the trial ends. It could take some time for the treatment to become available on the market if it is found to work, and longer again to be provided by a healthcare service. This is due to the length of time that a drug can take to be approved once a trial has finished.

At the end of a clinical trial, the results should be made available to all patients who are interested in knowing. They will also be published so that doctors and scientists know what the results were. However, full results of the trial are not always available right away, as researchers need to analyse all the results as accurately as possible, which can take some time.

Clinical Research Explained

Information about what clinical trials and observational studies are. Understand why you might want to take part in clinical research and why diversity in clinical research is important.

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