Clinical trials & medical research

Deciding not to take part although eligible to take part in a clinical trial

Everyone who is invited to take part in a trial is free to decline – to say no and should not feel under any pressure to take part. You are also free to leave a trial at any time and without giving a reason; (see ‘Withdrawing from a trial’). Reasons for deciding not to take part in a trial can vary from person to person, and it has to be what feels right for you at the time. It is important that if you decide not to take part in a trial you are told what the alternatives would be. If you are ill you will be given whatever is the normal standard care.

The majority of young people we talked to were happy to take part in clinical trials to help themselves and other young people with similar conditions, and help advance knowledge and medical science. (See ‘Reasons for wanting to take part: personal benefit’ and ‘Reasons for wanting to take part: helping medical science and others’.) 

A trial may involve invasive procedures and tests, and young people and their parents may worry about this. Making the decision to take part, or not to take part, is important and once you have been invited you should be given time to make a decision and the opportunity to ask questions. (See ‘Being invited to take part in a clinical trial: information and questions’ and ‘Making the decision to take part and giving assent and consent’.) 

Robert explained that when he was younger he didn’t take part in any research that involved extra blood tests, and that it’s OK to say No if the trial involves a procedure you are worried about. Nowadays he takes part despite some uncomfortable procedures.

Healthy volunteers may also say no to a trial if they are worried about invasive procedures or about being exposed to the risk of side effects (for example, from a new vaccine). 

Some people may choose not to take part because they know they have a preference for a particular treatment. Mohini, aged 12, was diagnosed with acute lymphoblastic leukaemia when 9 years old. It was a huge shock to her and her family. At the time Mohini was very poorly and didn’t understand too much about what was happening. Mohini’s parents were invited to enrol her in a trial of treatment for leukaemia. It was a randomised trial and Mohini would have been allocated to either the usual/standard treatment group or the new treatment group. 

Randomised trials are done when we don’t know which treatment is best, in other words when the relative merits and disadvantages of different treatments are uncertain. It is important to realise that, on average, new treatments are as likely to turn out worse as they are to turn out better than existing treatments. This means that, going in a trial, everyone, regardless of which of the treatment groups the computer allocates them to, must have similar chances of a good outcome. If, in spite of the treatment uncertainties that the trial has been designed to address, people would strongly prefer one of the treatments being compared, they should not volunteer for the trial.

Mohini’s parents discussed the trial with Mohini and with the doctors at the hospital. They had plenty of information to read and opportunities to ask questions. They were also given time to make a decision. Mohini’s parents decided that Mohini should have the final decision.

All the young people we talked to discussed taking part in a trial with their parents. Together they considered the risks and benefits of taking part in a trial especially when a trial involved testing a new drug or treatment that has not been fully tested in young people before. Many trials compare a new treatment with the current standard treatment by setting up two groups of people. One group of people will receive the new treatment and one group will receive the current standard treatment. If no standard treatment exists a placebo may be given. (See ‘Understanding about allocation (randomisation) to a treatment comparison group’).

In Mohini’s case, the trial has been completed and the results published. The results of the trial found that the new treatment is somewhat better than the standard treatment. (See ‘Why do we have clinical trials in children and young people’ and ‘Getting feedback and when the trial ends’.)

All trials have a set of guidelines about who can take part. These guidelines are called eligibility criteria. They ensure that a trial includes the people considered likely to benefit from the treatments and to protect participants from avoidable risks. The inclusion criteria help researchers decide who can take part in a trial, and the exclusion criteria indicates who should not take part. 

Sometimes tests are done to see if you are eligible and to ensure that you are unlikely to be harmed by treatment.

Katie aged 13 was invited to take part in a randomised trial to test a new medicine for cystic fibrosis. She had lots of different tests to make sure she met the eligibility criteria. She says it didn’t take long for the tests and she only had to wait a month before she joined the trial.

If you experience poor health during a trial you may be advised to stop until you are better. In most cases you will be able to re-join the trial when you are better, but you may have more tests to ensure you are eligible again.

If you have taken part and completed previous trials you may be approached to take part in another trial. However, you will still need to meet the eligibility criteria and you should always be given plenty of information and the opportunity to ask questions. You should also be given time to make a decision to take part, or not to take part.

If you are taking part in a trial you may not be eligible to take part in another trial at the same time. This will often depend on the trial and the research protocol (a detailed plan of the research investigation).

Last reviewed March 2017.


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