The features of a Phase III trial which help to ensure the maximum safety of patients are as follows: There are usually increased tests to monitor for side effects and safety of a new treatment and to compare it to side effects and safety of the older treatment. Usually enough is known about a new drug by this point to indicate what the most likely types of side effect concerns and differences there may be. A phase III trial often is the best opportunity to learn about possible delayed side effects of treatment, so that patients on these studies may be assessed at visits for years after their treatment is complete. Again, patients entering the study must have quite good organ function at the start so that the chance of dangerous side effects is reduced. There may again be a limit as to what type or how much prior treatment a patient has had, again to limit the risks of serious side effects for them.

Often, although there is a plan to enrol a set number of patients on a study, there will also be a plan to analyze the partial results at a set time or times during the study, with a rule that the study must be stopped if there is already a very clear and significant difference in the effectiveness or safety of one of the treatments being studied. In this case, there is usually a group of experts, called an Independent Data Monitoring Committee, who analyze the early results in this fashion, and decide whether the study should be stopped early. This helps to protect patients, as much and as soon as possible, from being offered a treatment that is less effective or less safe.

Learn more about the features of a Phase III trial.