Clinical trials

Medical research trials that involve patients are called clinical trials.

The aim of clinical trials is to compare different treatments to see if they work and how well they work compared to what is currently available to patients. There are different types of clinical trials, looking at prevention, diagnosis, treatment and quality of life. 

Some clinical trials test new treatments but others involve new ways of using existing treatments. For example, by comparing different doses, timings and treatment combinations to see what works best.  

This page tells you how you can find a trial and what things to think about before you give your consent to take part in a trial. We've also suggested some questions you might like to ask. 

Finding a trial

Researchers that run clinical trials look for people who meet a list of conditions.

Conditions might include having a certain stage or type of bowel cancer or having had a specific treatment before. If you'd like to take part in a clinical trial, ask your healthcare team if you're suitable for any current trials in your area.

You can also find a list of trials on the Be Part of Research and the Cancer Research UK websites. 

What are the different phases of treatment trials? 

Treatment trials go through multiple phases to test whether they are safe and if they work. All new cancer drugs are tested in the laboratory before they are given to people. 

Phase 1 trials involve a very small number of people in a specialist research unit. They aim to find the most appropriate dose might be and what the potential side effects are. If the drug is effective and a safe dose is found after several phase 1 trials, it could progress to phase 2.

Phase 2 trials also involve a small number of patients, but they aim to find out how well the treatment works and which types of cancer it is most effective for. They may also check the best way of giving the treatment, the ideal dose for effective treatment and the side effects and consequences of this pattern of treatment. 

Phase 3 trials compare how well the treatment works compared to current treatments. This phase often involves much bigger groups of patients from many different hospitals, often in different countries. They can gather much more information about the treatments including how well they work and the side effects patients experience. Phase 3 trials often last several years or more. They often involve 'randomisation'. 

Phase 4 trials look at the long term risks and side effects of a treatment, They happen after a drug has been given a licence which proves that it is safe and effective for patients. Phase 4 studies are not required for every medicine. 

What is randomisation?

Randomisation is a way of randomly assigning people to different treatment groups. If the new treatment is not being compared to a current treatment, it may be compared with a placebo (dummy treatment). Randomisation aims to make sure any difference in results is due to the treatment received. 

Taking part in a trial

The advantages of taking part in a clinical trial include:

• possibly having access to a treatment that isn't normally available 

• having extra check-ups and support 

• helping to improve treatment and care for people in the future 
   

The disadvantages include:

• possibly not knowing whether you are having a real drug or a dummy (placebo) drug 

• finding the extra check-ups tiring or difficult to fit into your everyday life 

• possible more tests, such as blood tests 

• the risk of unknown side effects 

The research team may send you a copy of the results once the trial is finished. 

Giving your consent

If you decide you want to take part in a clinical trial, you'll need to sign a form to give your informed consent. This means that you understand what the trial involves and you agree to take part.

You'll usually have time to ask questions about the trial and to speak to your family and friends before you decide whether to give your consent. If you change your mind, you can leave a trial at any time without giving a reason. 

If you decide to take part in a trial, the research team will send details to your GP and hospital healthcare team.

Nobody else will have access to your medical information. The trial results will not identify you or give any personal details about you.

Cancer Research UK has detailed information about taking part in clinical trials. 

Questions to ask

The research team will give you detailed information about the trial before you agree to take part and they will answer any questions you might have. Here are some suggested questions: 

• What is the trial testing? For example, a new treatment or combination of treatments? 

• How long will the trial last? 

• How long will the follow up period be? 

• Will I need to visit a hospital or GP for follow up or can it be done via telephone? 

• Will I know which treatment I’m getting? 

• Does the trial include a dummy (placebo) drug? 

• What are the benefits and risks of taking part in the trial? 

• Can I continue having the new treatment if the trial is successful? 

• What support will I get during the trial? 

• What treatment would I get if I decide not to participate in the trial? 

• What expenses can I claim? 

• Will I still see my usual healthcare team during the trial? 

• Can I have a copy of the trial results? 

 
Updated November 2025  

Next review November 2028