How Clinical Trials Work

What's in these pages?

This information sheet tells you more about how trials work, what to ask, and who to speak to if you are interested in joining one.

It includes:

  • Why take part?
  • How are they set up?
  • What are their risks and disadvantages?
  • Who can take part?
  • Recruitment to trials
  • Checklist of what to ask
  • Can I join one in the UK?
  • Can I join in another country?

Clinical trials are rigorously controlled tests designed to examine the safety and / or effectiveness of medicines, devices, treatments, or preventive measures in humans.

People have a number of different reasons for joining them. These may be:

  • to benefit from new research developments and any potential treatment as soon as possible – however, although the start of a clinical trial is a very promising sign, it isn’t a guarantee of a successful outcome or ongoing treatment
  • to ensure close monitoring of their condition as clinical trials use even more stringent assessments than usual, even after the trial has finished. This close attention could result in better management of the condition
  • to be part of pushing out the boundaries of scientific discovery – it may not benefit them, but it may benefit others


How are clinical trials set up?

A clinical trial must be carefully designed to ensure the safety of the participants, as well as answer specific research question(s). The length of a study varies depending on what is being studied. 

Each clinical trial follows a strict ‘protocol’ which describes its aims, design and organisation. This also provides information about the background, any pharmaceutical or other sponsors, reasons for the trial, and outlines the study plan. It also describes:

  • the type of participant who is eligible
  • the schedule of tests
  • what procedures will be involved
  • the medication(s) and dosage(s)
  • how long the trial will last

Participants are told how long the study will last before they enrol. They may be enrolled in any of the following trial ‘phases’:

Phase I - Aims to test the safety of a new treatment / medicine and see how well it is tolerated. These studies are often carried out on a small number of volunteers (usually healthy).

Phase II – Involves tests on a larger number of people with the condition to monitor how well a treatment / medicine performs.

Phase III - Involves an even larger number of people with the condition and follows the same process as Phase II. The aim is to gain a more in-depth understanding of how effective and beneficial the treatment / drug is.

Phase IV - Takes place once a new medicine / treatment has passed all the previous stages and has been given marketing licences. A marketing licence means the medicine can be made available on prescription. The safety, side effects and effectiveness of the medicine continue to be studied while it is being used in practice.


Who can take part?

All clinical trials have guidelines or ‘eligibility criteria’ which describe who can take part. These are listed in the clinical trial protocol.

  • Inclusion criteria’ describe factors that allow someone to participate in a clinical trial.
  • Exclusion criteria’ are factors that disqualify someone from participating.
Eligibility criteria are generally based on factors such as age, gender, the type and stage of a disease, previous treatment history and other medical conditions. They are used to keep the participants as safe as possible. For example, some underlying conditions could make participation in the trial dangerous

Eligibility criteria are meant to ensure that everyone taking part has similar symptoms at the beginning of the trial. This increases the reliability of the results. Without them it would be difficult, if not impossible, for the researchers to interpret the results because they would not know if the reason one person responded to treatment and another didn’t was due to the drug, or that it was a result of differences in their condition to begin with. This is especially helpful in the early phases of a clinical trial when there are often only a few participants. It’s also essential to be able to give robust evidence about a treatment’s performance when / if there is an application from the pharmaceutical company to regulatory authorities to assess whether to grant the treatment a marketing licence.


What are the risks and disadvantages of clinical trials?

It’s very important that anyone considering joining a trial understands what is involved. Before committing and giving consent to take part, they should have a very detailed discussion about the study with the trial nurse or doctor and explore any possible risks or disadvantages. 

The main disadvantage is that studies often involve multiple and frequent visits to a hospital, which may not always be easy or practical. Also, some procedures could be painful, for example injections and biopsies. There is also a risk of adverse reactions to the treatment.

Additionally, trial participants have to keep in mind that, although a treatment may prove beneficial in the long run, the treatment they personally receive might not provide any direct benefit for them. For example, there is a chance they might be given a very low dose of the drug, or even a placebo. A placebo is a harmless substance that should have no effect on the progression of a disease. It is used instead of a drug in clinical trials to help rule out any benefits a drug might appear to have because the person believes it will have an effect.


Recruitment to trials

To help someone interested in a trial decide whether to take part, researchers provide information so that they understand the risks and potential benefits, as well as any alternatives there might be to joining the trial. In general, before joining, any potential participant must sign an ‘informed consent document’ to show that this has all been discussed with, and understood by, them. Signing the informed consent document isn’t a contract. Participants may withdraw from a study at any time, even if the study is not over. 

In addition to this document, potential participants may also be given recruitment material, verbal instructions and take part in question-and-answer sessions and activities to measure their understanding of what they have been advised.

In most circumstances, because they will need to be monitored frequently, people who wish to participate in a trial will find it easier if they live relatively near the team which is conducting the research. Clinical trial organisers will usually, within reason, reimburse travel costs.


'Checklist’ of what to ask if considering joining a trial

It’s important that you feel comfortable to ask members of the healthcare team questions about the trial.

You may find it helpful to discuss:

  • The purpose of the study
  • Who can take part?
  • Why researchers believe the experimental treatment being tested may be effective
  • If the treatment has been tested before
  • What kinds of tests and procedures or treatments are involved
  • What you will have to do
  • Any possible risks, side effects, and benefits of the study
  • What would happen if you had an adverse reaction to the treatment
  • How the trial might affect your daily life
  • What effect it may have on your family
  • How long it will last
  • Where it will take place
  • How long each treatment will take and if a stay in hospital is needed
  • How often you will have to visit the hospital or clinic
  • Who will pay for the experimental treatment
  • If you will be reimbursed for other expenses
  • What type of long-term follow up care is part of this study
  • How you will know if the experimental treatment is working
  • Whether you will be given the results of the trials
  • Who will be in charge of your care
  • How this will all fit in with your regular care


How can I participate in a UK clinical trial?

To find out about the current clinical trials in SMA, please click here

To date in the UK, SMA clinical studies have involved very small patient numbers. The clinical leads from Great Ormond Street Hospital (GOSH) in London and the John Walton Muscular Dystrophy Research Centre in Newcastle have been able to recruit from their own known group of patients and, if required, have been able to reach out to colleagues in different neuromuscular centres. Therefore, in a sense, the possibility of inclusion in a trial has been largely influenced by who a person’s clinician is and their ability and means to travel. This seems hugely frustrating and an inequitable ‘postcode lottery’, but is possibly difficult to avoid due to the limited number of neuromuscular centres of excellence that have been clinical trial sites and the small numbers of participants.

Clinicians are very aware of how this must feel to families.

If you want to get involved in trials, do make sure your medical team knows about your interest. There is a robust National Network of Neuromuscular Clinicians and Physiotherapists, and upcoming trials are communicated to the Network in a timely way to give the possibility for your team to refer you if you are potentially eligible.

It’s also important to have your name and details recorded with the SMA Patient Registry as they may also be asked to help identify potential recruits should the inclusion criteria be very specific and limited. You can register at: but please note that being registered doesn’t mean a guarantee you will be invited for screenings for trials.

Also, if you are aware of a study coming up and you think you would meet the criteria, you can contact the centre involved directly. They, in turn, will then contact your medical team whose involvement is essential.

On a final note, the demand for SMA trials has been very high and cannot be fulfilled with only two clinical trial centres in the UK (London and Newcastle). Other neuromuscular centres would also like to offer trials, but further work is needed on how this can happen.


Can someone with SMA join a clinical trial in another country?

If you do want to try to do this, we suggest you:

Talk to your UK medical team about:

  • Their health and any risks of regular travel for the trial treatment to wherever you select
  • What, if any, effect this might have on their treatment and care by the NHS in the UK and access to any other NHS and social care services and support

Ask the trial Centre you are considering the questions suggested in the checklist.

You might also want to consider:

  • Travel insurance to cover their health needs. An initial conversation with the trial centre would be important to establish what, if anything, is already offered 
  • Managing this commitment to the trial - practically, emotionally and financially
We hope this summary has given a helpful overview of what trials involve and the possibilities they offer. If you do decide to join one, we hope that it has a positive outcome for you.


Version: 1.1
Author: SMA UK Information Production Team
Published: September 2018
Last updated: March 2019
Next full review due September 2021


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