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. 

 

The ethics committee
Stopping trials early

Long term results
 

 

A data monitoring committee (DMC) is usually set up before a trial starts. It looks at the safety and design of the trial. The DMC regularly checks the progress of the trial at specific times set out in the protocol. 

 

They look at things such as:

The DMC then recommend that the trial:

The ethics committee also keeps an eye on how the trial is going. The research team must tell the committee if patients in the trial have any unexpected side effects.

 

If the ethics committee needs to, they can:

Stopping a trial early means that the trial will close to recruitment. Trials can be closed early if:

• it’s clear that the trial treatment is obviously much better than standard treatment
• the trial treatment is much worse than the standard treatment 
• people are having severe side effects from treatment

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. This may not be the case in the long term.

A trial can also close 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.

 

The data monitoring committee may suggest that 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.

 

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 allows the research team to:

Good practice guidelines on the recruitment and involvement of public members on trial and study steering committees. Version 1.1
National Institute for Health and Care Research (NIHR)
NIHR website, April 2021
Accessed July 2025