Most clinical trials run as planned from beginning to end. But sometimes trials are stopped early. For example, the Institutional Review Board and Data and Safety Monitoring Board may stop a trial if participants are experiencing unexpected and severe side effects or if there is clear evidence that the harms are outweighing the benefits.

In some cases, a trial might be stopped because:

  • It is going very well. If there is clear evidence early on that a new treatment or intervention is effective, then the trial may be halted so that the new treatment can be made widely available as soon as possible.
  • Enough patients cannot be recruited.
  • The results of other trials have published that answer the research question or make it irrelevant.

Reproduced with permission from NIH’s National Cancer Institute. NIH does not endorse or recommend any products, services, or information described or offered here by Healthline. Page last reviewed June 22, 2016.