Phases And Types Of Clinical Trials: Overview

Clinical trials (also called clinical studies) test new ways to diagnose, treat, and prevent health conditions. These trials allow doctors and medical researchers to investigate drugs, devices, and techniques to ensure their effectiveness and safety.

Different types of clinical trials address certain issues and questions that researchers want to find the answers to either approve or disregard a new treatment approach.

A clinical trial is conducted in phases. Knowing the current phase of a clinical trial can tell you how close the researchers are to getting treatment or drug approved or re-approved for use.

What is a clinical trial?

A clinical trial is a medical research study that evaluates:

  • New medications or drugs

  • Medications or drugs that have already been approved

  • Medical devices

  • New forms of treatment and therapies

The aim of a clinical trial is to find effective ways to diagnose, evaluate, prevent, and/or treat disease.

Clinical trials allow doctors and researchers to determine whether a certain treatment, procedure, or device works on humans, is reasonably safe (the benefits outweigh the risks), and is more effective than treatments that are currently available.

The different phases of clinical trials are designed to answer different questions to find solutions for certain issues while providing maximum safety for trial participants.

What is a preclinical trial?

Preclinical studies are essential for determining whether a drug is ready for a clinical trial. Before testing a new treatment method on humans, it's important to understand the risks. Preclinical trials are used to determine the efficacy of a drug, the safe starting dose, and any potential adverse effects.

During a preclinical trial, the drug can be tested in the following ways:

  • In vitro – In a test tube or cell culture

  • In vivo – Tested on animals

  • In silico –  The study is performed on a computer or via a computer simulation (this method of testing is used in some but not all cases)

Once preclinical trials have been completed, a clinical trial can begin.

Phases of clinical trials

Each clinical trial is comprised of various closely connected phases. Each phase has a specific purpose and helps medical researchers to answer certain questions. One phase needs to be completed before proceeding to the next.

Phase 0

The first phase of the clinical trial involves a number of healthy human participants (about ten).  Researchers give each participant a very small dose of a drug being tested, which is often referred to as a microdose.

Phase 0 usually takes about seven days. The main goal of this clinical trial phase is to understand how the body responds to the small dose of the drug and to determine if the drug behaves as expected based on preclinical microdosing studies. This phase can also help researchers identify viable candidates for further research early on in the trial process.

Phase 0 bridges the gap between preclinical testing and clinical studies.

The information gathered during phase 0 helps researchers to make decisions about further drug development earlier, which can reduce the overall costs of the clinical trial.

In some clinical trials, researchers skip phase 0 and proceed directly to phase I.

Phase I

During phase I, researchers test the drug or treatment on a small group of healthy human volunteers (up to 100). At this stage, they identify the safe dosage and evaluate any side effects.

At the start of phase I, participants are given a small dose of the drug. Researchers monitor each participant’s condition and any side effects they may experience. If the treatment goes well, the dose may be increased, depending on the aims of the study. This process continues until researchers determine the most effective dose with the fewest and/or least severe side effects. This phase usually lasts for several months.

In some cases, phase I can be either shortened or skipped. This can happen when a drug that has previously been approved for treating another disease is being studied for its potential to treat another condition.

The success rate of phase I clinical trials is about 70%¹. It means that 70% of medications pass the trial and proceed to phase II.

Phase II

During phase II of the clinical trial, the drug or treatment is then tested on a larger group of volunteer participants (100–300). All of the participants are patients with a medical condition that researchers expect that the treatment being tested will address. Participants are given a dosage of the drug that researchers determined to be safe during phase I of the clinical trial.

The goal of phase II is to evaluate the appropriate dose and treatment regimen for patients with a specific condition. At the same time, researchers monitor participants for any side effects that may not have arisen during phase I.

Phase II tends to be divided into two parts:

  • Phase 2a – focused on dosage

  • Phase 2b – focused on efficacy

Phase II usually lasts between several months and two years, and it has a success rate of 33%.

Phase III

Phase III of a clinical trial usually involves 300 to 3,000 volunteer participants who have the condition the drug or treatment is intended to treat.

During this phase, participants are divided into two groups:

  • The group that receives the new treatment.

  • The control group that receives either the currently approved care or a placebo.

Patients who participate in phase III are usually not made aware of which group they are in and which treatment they are receiving. This helps researchers to ensure the credibility of the study and get a better picture of the effectiveness of a treatment compared to existing options, or no treatment at all.

The goal of phase III is to determine the effectiveness of a treatment and its safety rating. If this phase is considered to be successful, the company conducting the clinical trial can seek FDA approval for the drug or treatment. If FDA approval is given, doctors can start to prescribe the treatment to their patients. Once that happens, phase IV begins.

The success rate of phase III, which lasts between one and four years, is 25%–30%.

Phase IV

Phase IV involves participants who are patients seeking treatment for the specific condition that the treatment addresses. The aim of this phase is to determine the long-term effectiveness and side effects of the treatment being trialed. It can also help researchers to discover whether the treatment has the potential to help with other conditions.

Phase IV continues while the treatment is available on the market, which essentially means it is ongoing.²

How to participate in a clinical trial

If you have a medical condition and want to participate in a clinical trial that is focused on your condition, you can search for available trials that match your criteria. The benefits of participating in a clinical trial include:

  • Gaining access to the latest treatment opportunities before they are made available to the general population. These newer treatments may be better at treating your condition or have fewer side effects. 

  • An opportunity to become actively involved in managing your health by learning more about your condition and treatment options.

  • Contributing to new treatment development which could help many other patients.

  • Receive closer monitoring of your condition or care, as the nature of a clinical trial is that you will have medical professionals assessing you throughout the study.

Make sure to take your time to research all available options and read their descriptions and participation requirements. In many cases, you may need to be under continuous observation during the trial, so it could interfere with your work, studies, or travel plans.

Before making a decision to join a clinical trial, it's important to speak with your doctor about whether it is right for you.

It is also important to remember that there is no guarantee that you will directly benefit from participating in a clinical trial.

HealthMatch makes it easy to find a suitable clinical trial.

The lowdown

The overall aim of a clinical trial is to test different medications, drugs, devices, therapies,  or other treatments to determine if they are safe and effective at treating certain conditions. There are different types of clinical trials depending on the questions researchers are looking to answer. Each clinical trial is made up of various phases which are designed to optimize the testing, research, evaluation, and approval processes. A successful clinical trial will result in a treatment being considered effective and made available to the general population.

If you are interested in participating in a clinical trial, speak to your doctor about whether this is appropriate for your condition and personal factors.

  1. Step 3: Clinical Research | U.S. Food and Drug Administration

  2. Phase IV of Drug Development (2010)

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