Many clinical trials (especially for new drugs) take place in a number of stages, or phases. For example, when a new treatment is first developed, such as a new drug, it will be tried first in a few people to get an idea of how safe it actually is. They may be healthy volunteers, who are given a compensation payment for taking part, or they may be people who are ill, and could be patients who have already tried all the usual treatments. This is called a Phase 1 trial. At this stage, the treatment is usually given to all those taking part, and it is not being compared against some other treatment. By the time a drug reaches Phase 2, researchers will know more about it. In Phase 2 the aim is to test the new drug in a larger group of people to get a better understanding of how safe the drug is and to better understand any side effects and also to see if there are signs of helpful effects in patients. Phase 2 trials may or may not involve a comparison with another treatment. In Phase 2 trials researchers can start to get an idea of whether a treatment works for some people, and what kind of side effects they experience. But at this stage the numbers of people included are still too small to give researchers the firm evidence they need about the treatment’s effects and that any observed change is not just happening by chance. This is why Phase 3 trials are needed.

Phase 3 trials are usually large and may include hundreds or even thousands of patients. They often compare the effects of newer drugs or treatments with standard treatments if there are any. They provide a better test of whether new treatments work better than existing treatments, and stronger proof about how common and serious any side effects are.

Almost all Phase 3 trials are normally called randomised clinical trials (RCTs):

Randonmised
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This is where participants are randomly allocated for a trial group, this happens regularly in research trials and is considered to be good practice in terms of achieving results that can be trusted.

Control Randomised
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A study in which researchers choose people at random is an RCT, one group of people, the experimental group, is given the new treatment. The other group, called the control group, is given the standard treatment. If no standard treatment exists, the control group may not be given any specific treatment or may be given a placebo. Some trials may compare more than two groups.

There are also several ways in which the results of trials can be made as reliable and accurate as possible. One of these is to make the trial a ‘blind trial’. In a blind trial the participants are not told which group they are in. This is because if they knew which treatment they were getting it might influence how they felt or reported their symptoms. Some trials are double-blind, which means that neither participants nor the researchers, doctors and others treating them know which people are getting which treatments. This also avoids the researchers’ anticipating and influencing the results of the trial.

Randomised double-blind crossover trial
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The important part of this is the “crossover” which means that both groups receive the treatment and both groups receive the placebo. Patients then swap over to receive the placebo or treatment. As it is double-blinded which means that neither the researcher nor the patient knows which treatment the patient is having. This is considered to be the very best way to determine how useful an intervention or treatment is because it is thoroughly tested.