Benefits and risks of clinical trials

There are benefits and risks to taking part in a clinical trial. But the trials are made to be as low-risk as possible while making the benefits as great as possible for anyone who takes part.

You can speak to your doctor before deciding whether to take part in a trial and ask them any questions you might have. You may want to know:

  • more about the trial
  • what you will need to do.

You may also want to think about practical issues around taking part in a trial. You might have to visit the hospital more often, which could mean extra travel costs.

During and after the trial you’ll be followed up carefully. This means you may need to have regular tests. For some patients this is reassuring. Others would prefer not to have more hospital visits and not take part in the trial.

There is no right or wrong decision about taking part in a trial. To help you decide, you could talk to family or friends, or write down a list of the pros and cons.

Benefits and risks of taking part in a trial

Clinical trials are designed to make the risks as low as possible and the benefits as great as possible for all the people who take part, whichever treatment they get.


Taking part in a trial means that you may be given a new treatment that works better than the standard treatment. The new treatment might not otherwise be available yet because it does not have its license. You’ll also be helping doctors find out which treatments may benefit future patients.

When you take part in a trial, you’ll be followed up very carefully during and after the study. Your doctors will probably want you to have regular tests, such as blood tests, and you may be asked some extra questions about how you’re feeling. This means that any changes in your health – whether or not they are related to the treatment you’re having – can be noticed and dealt with as soon as possible. Some patients find this reassuring. Others would prefer not to have more hospital visits and therefore would rather not take part in trials.

Potential risks

With any clinical trial, there is always a small risk that the treatment could harm you or that you could experience side effects that are unpleasant or unexpected. During the trial, researchers make every effort to minimise these risks.

Practical issues

Taking part in a trial may mean going to your hospital or GP more often than you would normally, so bear this in mind before you agree to take part. Attending the hospital can be tiring and the extra travel may cost a lot of money. Ask your doctor how many extra visits will be needed and think about how convenient this will be for you. You can also ask whether the research trial will pay for your additional travel costs, and how you can claim.

Making a decision

If you are finding it difficult to decide whether or not to join a clinical trial, it may be helpful to talk things through with your doctor or nurse. You might also find it helpful to speak with your family and friends as they may be able to help talk things through with you. Sometimes something as simple as writing a list of pros and cons can be helpful.

It is important to know there is no right or wrong decision. Any decision you make will be the right one for you at the time. If you need more support, you can call the Macmillan Support Line on 0808 808 00 00 to talk to our cancer support specialists.

We have more helpful information and advice about making treatment decisions.

Questions to ask

Here are some questions you might like to ask before deciding whether to take part in a trial. Your doctor or nurse will probably answer most of these when they tell you about the trial. Most of these will be covered in the written information you are given about the trial.

General questions

  • What is the trial called?
  • What is the aim of the trial and how will it help people?
  • Why have I been invited to take part?
  • What are the treatment choices in the trial?
  • What are the benefits of the trial for me?
  • What are the possible risks?
  • How long is the trial expected to last?
  • Can I withdraw from the trial at any time?
  • The answer should always be yes.
  • What happens if I leave the trial early?
  • How long will it be before the results of the trial are known?
  • Will I be informed of the results?

Remember that it may be some time before the results are available. It’s not unusual for trials to take many years before the results are available. While doctors may see quite soon whether people respond to a new treatment, it will take much longer to see how long the response will last.

Practical questions

You may also want to ask some practical questions to make sure you’re happy with any demands that the trial will make on you:

  • How much of my time will be needed?
  • Will I need to take time off work?
  • Will I need extra help from family and friends?
  • Will my fares to and from the trial centre be paid?
  • If so, how can I claim the costs back?
  • What extra tests or appointments will I have?
  • Will I have to collect the drug from the hospital?
  • Will the drug be sent to me by post or will I get it through my GP?
  • Will I have to fill in questionnaires or keep a diary? Sometimes questionnaires are simple tick-box lists, or you may be asked to record your answers online.

Back to Can and should I take part?

Safety in clinical trials

All clinical trials must meet high standards of practice, be approved by an ethics committee and closely monitored for safety.