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Patients Clinical Trials Phase I-IV

Phase I

Phase I trials primarily determine how a new drug works in humans, help to predict the dosage range and involve between fifty and one hundred healthy volunteers.

Phase I trials are short and volunteers are closely monitored at the research centre where the trial is being conducted.

The principal objective of Phase I trials is to assess what effect the experimental drug has in the human body - what happens to the drug once released in the human body and how the human body reacts to the drug.

The goal of Phase I trials are:

  • to assess the safety of the drug,
  • to determine the side effects of the drug,
  • to evaluate how the drug should be administered.


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Phase II

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Phase II trials test for efficacy as well as safety in a group of between one hundred to three hundred patients with the condition for which the medicine has been developed. Healthy volunteers are not included. Several Phase II trials are generally performed to test the drug in different patient populations and in different indications. Patients are closely monitored in Phase II trials but do not need to stay at the research centres.

The goals of a Phase II trial are:

  • to assess short-term efficacy and safety of the drug,
  • to determine the optimum dosage range for the drug (that is, find the dose at which the drug has the greatest efficacy with the least side effects).


Phase III

Phase III trials involve a much larger group, between several hundred to several thousand patients, to help determine if the new drug can be considered both safe and effective under mid to long-term assessment.

The goals of a Phase III trial are:

  • to confirm the safety and efficacy of results obtained during Phase II trials,
  • to compare the new drug to other compounds either with a placebo (an inactive version of the new drug) or other standard therapies, to see if the new drug out-performs its competitors.

Phase III trials may also be used to assess the efficacy and safety of the new drug when given in combination with other approved therapies.

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Phase IV

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Phase IV trials are conducted after the new drug has been granted a licence. In these studies, the new drug is prescribed in an everyday healthcare environment which allows results to be developed using a much larger group of participants.

Phase IV trials enable new uses for the new drug to be developed, comparisons with other treatments for the same condition to be made and to determine the clinical effectiveness of the new drug in a wider variety of patient types. Safety is a major part of Phase IV trials which often involve several thousand patients so that more rare side effects, if any, may be detected.