Clinical Trials and their Phases

Clinical Trials are important for both the patient and the medical research community. A clinical trial is a process in which a large number of people with a certain disease are given a new or old drug or device for a specific purpose. Clinical trials have been conducted for several different drugs and devices.

What is a Clinical Trial?

To begin with, a clinical trial is a scientific method of studying the safety and effectiveness of a drug, medical device, or other medical intervention. The purpose of a clinical trial is to determine whether a drug is safe and effective for a specific use or to determine the effectiveness of treatment. The data from these trials can be used to improve the current standards of care, develop new drugs, and create more precise health statistics.

The FDA requires all new drugs and medical devices to be tested before they can be approved for sale.

Groups in Clinical Trials

In a clinical trial, the subjects are usually divided into 2 groups. This includes an experimental or test group and a control or comparison group. The experimental group are those who are given an intervention, while the control group are those who are given a usual treatment or a placebo.

The term placebo is a medical term referring to an inert substance used to treat a disease or condition and is frequently used  in clinical trials.

Phases of Clinical Trials

Clinical trials are the primary method of determining whether new drugs or treatments are safe and effective. They are usually conducted in four phases. Each of these phases of clinical trials has its own purpose.

Phase I

Firstly, phase I is the first part of the clinical trial, in which the experimental medication is tested on a small group of people. This is done in order to determine the safety and tolerability of the new medication.

  • The human subjects (often healthy males) are exposed to increasing single doses of a new drug to determine safe and acceptable dosing levels.
  • The toxic effects of the new drug, if any, are observed. A provisional safe dosage of the same is established.
  • Usually, the number of subjects is kept from 20 to 80, with a duration of approximately one year.

Read about clinical trials- Types of Clinical Trials – My Biology Dictionary

Phase II

As Phase I reveals that there are no serious safety issues, the trial proceeds to Phase II. It is the part of the trial where effectiveness is examined on a larger group of people.

  • It aims to determine whether the new drug is can be used on people who have a particular disease or condition.
  • Phase II continues to study the clinical efficiency and define the most appropriate dose(s) for a larger population
  • It is conducted on approximately 100 to 500 human subjects over the span of 2 to 3 years

Phase III

Thirdly, phase III trials are of prime importance in assessing the drug’s efficacy and safety of the treatment or new drug being studied. They require very careful and thorough planning and execution.

  • Phase III trials are often randomized. They take place at multiple centres around the world, studying different populations and suitable dosages.
  • Additional information collected from Phase III studies includes long-term tolerance of the drug. Moreover, it also includes the usage of a new drug in combination with other drugs and varying dosing schedules.
  • The number of subjects ranges from 1000 to 2000, often from varying demographics and across a wider range of age groups.

As Phase III is concluded, the data that was collected from the preclinical and clinical trials is summarized into a New Drug Application (NDA). The NDA is then submitted to relevant regulatory agencies such as the Food and Drug Administration (FDA). 

If the FDA agrees that the trial results are conclusive and positive, it will approve the experimental drug, device or treatment.

Average time for approval of NDA in USA is 2.5 years

phases of clinical trials

Phase IV

Lastly, phase IV studies take place post-FDA approval. It is important to continue studying the adverse effects of the new drug. In case it has been missed in Phase I-III, thus phase IV helps.

  • Phase IV studies extend the knowledge of the drug with regard to different patient populations.
  • It is vital to investigate the effects of long-term exposure on people with different conditions.
  • Results of Phase IV studies may also lead to new Phase I-III studies. This is for the same drug in a new indication.

Clinical trials do not end once the drug is approved.

phases of clinical trials


Clinical trials are rigorous tests of new drugs and medical treatments. During these trials, scientists test whether a new drug is safe and effective. Moreover, whether it is better than a placebo to improve symptoms. They typically test the drug on a group of people who are suffering from the disease or have a risk of developing it in the future.

phases of clinical trials

To summarize, conducting clinical trials is a key step in the process of bringing a new drug to the market. It can be costly and time-consuming. It is not uncommon for a drug trial to take years of work before it is ever completed. Each drug must pass smoothly through all the phases of clinical trials in order to be deemed ‘fit’ for the market. 
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Team MBD

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