How clinical trials are supervised

Trials are supervised at the planning stage and monitored right the way through. 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.

Once the trial is underway the committee looks at how things are going. This committee plans how often they want reports from the researchers. Usually this is once a year, but it may be more often.

The reports look at

  • How many patients have been recruited
  • How many patients have withdrawn from the trial
  • Any side effects the patients have had
  • Patient feedback about benefits and side effects
  • The results so far

The role of the committee

The data monitoring committee may decide to stop the trial early if any harm has come to patients – for example, if they have had bad drug reactions.

The committee looks at the early results of the trial. It then produces a short report recommending that the trial should

  • Continue as it is
  • Continue with some changes
  • Stop early
  • Run for longer

Reporting on side effects

Between the yearly reports, the researchers have a duty to tell the ethics committee about unexpected side effects. The ethics committee can

  • Stop the trial early or temporarily
  • Ask for a change in the trial plan (the protocol)
  • Ask for the patient information leaflet and consent form to be changed if needed

Stopping trials early

Trials can be closed early if the new treatment is giving such good results that it is obviously much better than the standard treatment. Then more patients have access to the new treatment sooner.

Researchers don't like to close trials early unless there is very, very strong evidence that one group of patients is doing much better than the other. Doctors have to be sure that the treatments they recommend have been fully tested.

In the short term, results may seem better for one treatment over another. But in the long term, this may not be the case. Closing a trial early can make it difficult to interpret the results.

Trials can also be closed early if the new treatment is giving much worse results than the standard treatment. Then, patients having the new treatment would be switched to the standard treatment.

A more common reason is that the trial is recruiting patients too slowly. The funding organisation may decide that a 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 than originally planned will need to take part in order to get enough results.

Follow up after treatment in a trial

The follow up period is the time after all the patients have been treated until the end of the trial.

Trials often go on for years after all the patients who took part have finished all their treatment. The researchers need to find out what the long term effects are. For example, they may check whether the new treatment keeps a cancer under control for longer than the standard treatment.

Trials may also monitor patients to see if there are long term side effects. They need to collect information about the patients for years to find this out.

You will probably not have to do anything during this time. It just means that your doctor will keep the researchers informed about what happens to you.

Related information

Read about what trial results mean.

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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