Here
you will find an explanation of what a randomised trial is and the
different phases of trials. Click on the links below to jump
to a topic:
Many clinical trials are randomised controlled trials
(RCTs). Clinical trials aim to make a fair comparison between
a new treatment and the existing treatment, or between two (or
more) existing treatments, to see which one works best.
A controlled trial compares two
groups of people: an experimental group who receive the new
treatment and a control group, who receive the existing
treatment or a placebo. The control group allows the
researchers to see whether the treatment they are testing is any
more or less effective than the existing treatment.
If you take part in a randomised
controlled trial, you will usually have an equal chance of
receiving any of the treatments being compared. The decision
about which treatment you’ll receive is random – based on
chance. A computer programme will allocate which treatment
you’ll receive, not you or the doctor. This is called
randomisation.
Randomisation ensures that the two groups of
people in a trial are as similar as possible, except for the
treatment they receive. This is important because it means
that researchers can be sure that any differences in outcomes
between the groups are therefore only due to the treatment.
Randomisation is also the best way of ensuring that the results
of trials are not biased by the way treatments are selected. For
example, if a doctor chose which treatment a patient should receive
as part of a trial, she or he might give the new treatment to
sicker patients, or to younger patients. This would make the
results of a trial unreliable. Randomisation helps prevent this
kind of bias.
Across the world, randomised controlled trials are now seen as
the most reliable way to test new treatments and to compare two (or
more) existing treatments, to see which one works best.
Back to top
New treatments usually have to go through a series of phases to
test whether they are safe and effective. New drugs go
through a number of different phases of trials:
- Phase I trials aim to test the safety of a new
treatment. They look at side effects of a treatment – for
example, does it make people sick, raise their blood pressure etc?
Phase I trials involve only a small number of people, who are often
healthy volunteers.
- Phase II trials test the new treatment in a larger group of
people who usually have the disease for which the treatment is to
be used, to see whether the treatment is safe and has some
effect. Usually less than one hundred people are involved at
this stage.
Treatments only move into a phase III clinical trial if phases I
and II have been successful.
At the MRC Clinical Trials Unit, most of the trials we run are
phase III trials. Phase III trials test the new treatment in
a larger group of people. They look at how well the new
treatment works, and at any side effects it may cause. Phase
III trials usually last longer than phase II trials.
In phase III trials, and sometimes in phase II trials, patients
are usually randomised to receive the new treatment, the current
treatment or sometimes a placebo.
Often several thousand patients will be involved in a phase III
trial. These trials may involve different hospitals in
different countries. At the MRC Clinical Trials Unit, we run
phase III trials across Europe, parts of Africa, South America and
the USA.
Phase III trials often need to involve large numbers of people
because researchers usually need to be able to measure quite modest
differences between treatments. The smaller the expected
advantage of one treatment over another, the more people will be
needed to take part in a trial.
Phase IV trials usually look at the overall risks and
benefits of a drug or treatment.
Back to top
Last Update Date : 7/6/2009
