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Types of clinical trials

Clinical trials

Clinical trials can be categorised according to their objectives and also the way they are organised. For example, they might be prevention trials, treatment trials or diagnostic and screening trials.

  • Interventional trials (also called treatment trials) are clinical trials which set out to test treatments or combinations of treatments which have not yet been officially approved. For example, a pharmaceutical company may have developed a new drug which it believes would be effective in the treatment of Alzheimer’s disease but must first test it on human volunteers in accordance with strict and rigorous guidelines in order to ensure that it is safe and effective. Some drugs might be aimed at curing a particular condition, whereas others might be aimed at better controlling symptoms of a particular condition.
  • Prevention trials involve tests to find ways to prevent particular medical conditions or if people have them already, to prevent them from reoccurring. The emphasis of these studies might be on medicines, vitamins and minerals or lifestyle changes.
  • Observational trials investigate health issues in large groups of people. The participants in such trials do not receive any treatment but may be asked to provide information, blood samples
  • Diagnostic and screening trials are aimed at finding new ways to detect and diagnose medical conditions (e.g. a better test, a more effective procedure or a more sophisticated tool).

Clinical trials can also be classed according to whether they are considered therapeutic or non-therapeutic.

  • A therapeutic trial is one in which the treatment under investigation is believed to be likely to benefit the participants in some way (at least those receiving the experimental drug - in the case of drug trials).
  • A non-therapeutic trial, on the other hand, is one which is unlikely to produce any direct benefit to the participants involved. The aim of a non-therapeutic trial is to obtain knowledge which may contribute towards the future development of new forms of treatment or procedure.

Finally, irrespective of whether they are therapeutic or non-therapeutic, clinical trials may be described as randomised trials, blind trials, add-on studies, open label trials or randomised double blind placebo controlled trials. These terms provide information about the way that the trials is organised which may have consequences for the subjects (mostly with regard to the inclusion of a placebo group which is fairly common. A brief description of some of these terms is provided below:




The people who volunteer to take part in the study (sometimes called participants or patients)


Subjects are randomly assigned to different groups

Open label

Subjects and researchers are all aware of the drug being given.


The subjects do not know which group they are in e.g. whether they are in the treatment group or the placebo group.

Double blind

Neither the researchers nor the subjects know to which group the subjects belong until it is revealed at the end of the study.


A substance which does not contain the active ingredients of the experimental drug but looks the same (sometimes called a dummy drug).


All subjects receive an existing treatment but some then receive the additional experimental drug whilst others do not or are given a placebo

Single centre

The study is carried out at one location


The study is carried out in several locations (i.e. different towns or even different countries)



Last Updated: Friday 21 August 2009