How clinical trials are monitored

Trials are checked at the planning stage and monitored all the way through to make sure the people taking part are safe. This page tells you about that process. There is information about

The data monitoring committee

A data monitoring committee (DMC) is usually set up before a trial starts. It looks at the safety and design of the trial. The committee also regularly check how things are going.
They look at things such as:
  • how many patients have agreed to take part
  • how many patients have decided to withdraw from the trial
  • any side effects people have had
  • patient feedback about benefits and side effects
  • any results so far
The committee then recommend that the trial:
  • continues as it is
  • continues with some changes
  • stops early
  • runs for longer

The ethics committee 

The ethics committee also keeps an eye on how the trial is going. The research team must tell the committee if people taking part in the trial have had any unexpected side effects.
The ethics committee can then:
  • stop the trial completely, earlier than planned
  • stop the trial temporarily while they decide the best thing to do
  • ask the research team to change the trial plan (the protocol)
  • ask the research team to update the patient information sheet and consent form 

Stopping trials early

Trials can be closed early if it’s clear that the trial treatment is obviously much better, or much worse, than the standard treatment. Or if it is causing severe side effects.
Researchers don't like to close trials early unless there is very strong evidence that one group of patients is doing much better than the other.  Closing a trial early can make it difficult to interpret the results. Sometimes results may seem better for one treatment over another in the short term. But this may not be the case in the long term.
A trial can also be closed early if it is recruiting patients much more slowly than expected. The funding organisation may decide that the trial is recruiting so slowly that it will take too long to come up with any results. In that case, it may not be a good use of funds. And it may not be ethical to carry on entering patients into a trial that is not going to decide anything in the long run.

Running trials for longer

The data monitoring committee may suggest the trial runs for longer than planned. They may do this if they think there is a possibility the trial can prove something useful, but that more patients are needed to get enough results.

Long term results

Researchers usually continue to collect information about patients who have taken part in a trial after they finish treatment. Sometimes they do this for several years.
This is partly to see how well the different treatments work in the long term. And partly to find out about any long term side effects.

Related information


Last reviewed

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

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