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Cystic Fibrosis Trust

How do clinical trials work?

Find out more about what it takes for a clinical trial to take place in the UK.

There are different types of clinical trials; many involve new medications, but others may look at prevention of illness, non-medication treatments, diagnosis and ways to improve quality of life.

For a trial to take place in the UK, two independent bodies have to give it approval: a Research Ethics Committee and the Medicines and Healthcare Products Regulatory Agency (MHRA). These bodies examine every aspect of the trial to make sure it's ethical, well organised and safe, and any potential risks are minimised.


Pre-clinical trial

Once approval has been given, a pre-clinical trial on human and animal cells, and often directly on animals, is carried out to test for safety. This pre-clinical trial, which is legally required, is designed to reduce the chances of serious adverse reactions when the treatment is trialled on humans.

Following a successful pre-clinical trial are four key phases:

Phase 1

The first phase assesses the treatment for safety and side effects, and is usually carried out on a small number of healthy volunteers. However, Phase 1 studies for CF do often involve people with the condition too.

Phase 2

This phase involves a small number of people who have the condition being treated. The second phase continues to assess for side effects as well as signs of effectiveness of the treatment. It may also be used to determine the optimal dosage.

The second phase may be split into two parts: Phase 2a and Phase 2b.

Phase 2a studies explore whether the medication has any degree of efficacy (whether it produces the desired or intended result) and what a suitable dose range might be, as well as assessing safety.

Phase 2b studies explore optimum dosage as well as efficacy and safety.

Phase 3

This phase involves a larger number of people with the condition, sometimes several hundred. This stage gathers more information about the effectiveness of the treatment and any side effects. Some treatments will become licensed after this phase. Those that don't move onto Phase 4 for further safety monitoring.

Phase 4

If the treatment has proved safe and shows signs of effectiveness after the first three phases, it may (but not always) proceed to Phase 4 to capture more information on efficacy and continue to monitor side effects and long-term risks and benefits. Effectiveness is also compared with similar, already licensed treatments.

The length of time from pre-clinical trials through to a product getting licensed can vary greatly, and may take many years.


We've made a short video that explores the drug development process and shows how drugs are approved for use after they have been through clinical trials.

Clinical trials FAQs

What are the risks in clinical trials?

Clinical trials are carefully controlled, regulated and organised to minimise risk to participants. Serious side effects are very rare and clinical trials are now safer than ever.

Every trial has an independent Data Safety Monitoring Board (DSMB), and if anything happens during a study, such as a bad reaction, it is immediately reported to the DSMB. The board will stop a trial if there is any doubt about the safety of the treatment.

Naturally, being involved in a clinical trial may involve some disruption to your day-to-day life, but research teams do their best to make sure you are inconvenienced as little as possible.

What is informed consent?

When deciding whether to take part in a clinical trial, it is important that you are provided with all the information you need. This will involve your CF doctor or a researcher talking through with you what the clinical trial will involve. You will also be given a Patient Information Sheet to take home and read. This will help you understand what taking part in the clinical trial will involve, and why the clinical trials is being done.

After you have had time to read the Patient Information Sheet and ask your CF doctor or researcher any questions you may have, you will be asked to sign a consent form that shows you understand what the trial involves and are willing to take part. This process is called 'informed consent'.

If you are interested in taking part in a clinical trial you should discuss it with your CF team. There is never any obligation to take part, and you should not feel under any pressure to do so. Whether or not you decide to take part will have no impact on the care you receive from your CF centre or clinic. You can withdraw from a trial at any time, without giving the reason why if you don't want to. This will not affect your treatment.

How can I get involved in an active trial?

We are committed to creating a space where all information on CF-related clinical trials is accurate and easily-accessible. While we are working on this resource, you can find out about current and upcoming CF trials by visiting the NHS National Institute for Health Research website, INVOLVE.

The Cystic Fibrosis Trust cannot guarantee that the information supplied by these external sites is accurate or up to date.

How can young people get involved in research?

Are you a young person with an interest in research? Take a look at GenerationR, a National Young Person's Advisory Group funded by the National Institute for Health Research (NIHR). You can join an advisory group near you, find out more about the organisation or take advantage of their resources. Take a look at the video below to find out more about getting involved in a clinical trial as a young person.

What is the Clinical Trials Accelerator Platform?

Clinical trials are essential to prove the safety and effectiveness of new drugs, and to make them available as quickly as possible. At the moment there aren’t enough opportunities for people with CF to take part in clinical trials, which prevents timely access to cutting edge therapies and treatments. To change this, we are currently setting up the Clinical Trials Accelerator Platform, where we are working with a number of CF centres to increase clinical trial opportunities for all people with CF.

Key terms


A placebo is an inactive or 'dummy' drug given to some patients in a clinical trial. The placebo has no medical effect and is used to determine the effectiveness of the real drug being tested.

Randomised Controlled Trials (RCTs)

In a Randomised Controlled Trial participants are randomly allocated to different treatment groups, such as a placebo or the drug being tested. RCTs make sure the results of the trial are as accurate as possible, removing any potential bias on the part of the patients or researchers. Most phase 2 trials are RCTs.

Blind / double-blind trial

If a trial is 'blind', the participant does not know whether they are receiving the treatment being tested or a placebo. In a 'double-blind' trial, neither the patient nor the research team knows whether the participant has been given the treatment or not; only those analysing the data will know who has received the real treatment. Blind trials (also called 'blinded trials') are designed to eliminate bias and ensure accurate results. 

Further information

You can find out more about clinical trials by reading Clinical Trials in Cystic Fibrosis: Information for Patients, produced by the European Cystic Fibrosis Clinical Trials Network.

We support the European Cystic Fibrosis Clinical Trials Network. The CTN works across large research centres in Europe to intensify clinical research in the area of cystic fibrosis and to bring new medicines to patients as quickly as possible. In the UK there are CTN centres in Belfast, Leeds, Nottingham, Birmingham and London.

Clinical Trials Accelerator Platform

Find out more about our UK-wide initiative to bring together existing CF centres to improve access, participation and delivery of clinical trials.

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Want to find out more?

Have a look at some useful clinical trials resources, from podcasts to getting involed in research surveys.

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Active trials

We are in the process of creating a trials database specific to the UK CF community. In the meantime you can search for active trials using the UK Clinical Trials Gateway.

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