When Are Phase 1 Clinical Trials Done?

The possible benefits of phase 1 trials has changed significantly

A Phase 1 clinical trial is the first phase of three or four phases of research studies used to test a new treatment on humans. The major goal of a clinical trial is to determine whether a drug or procedure is safe for human use. Prior to phase 1 clinical trials, a drug must be studied extensively on disease cells in the laboratory and/or in laboratory animals.

A med student taking notes for her thesis
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The purpose of clinical trials is to find treatments that either work better or have fewer side effects than treatments that are currently available. All medications that are approved to treat any condition were once tested in a clinical trial. And during that trial period, the only people who were able to receive the treatments were those who were enrolled in the clinical trial study group.

Definition and Purpose of Phase 1 Clinical Trials

Phase 1 clinical trials are done to see if an experimental drug or treatment is safe. After treatment is tested in the lab or on animals (called preclinical testing), it enters a phase 1 clinical trial that involves testing on humans. Preclinical testing is often extensive, and significant and positive results must be found in order to have a human trial approved.


Phase 1 clinical trials involve only a small number of people to determine if a drug or treatment is safe, the best dose of a drug, and how it should be given (such as orally, intravenously, or with another method). The participants may be divided into groups that receive different doses.

Though the primary purpose of these trials is to evaluate treatment safety, they may also track whether a treatment appears to be beneficial if the participants have a better outcome than what would be expected without the treatment.


Since phase 1 trials are the first studies to be tested on humans, they carry high risks. People enrolled in a phase 1 study are usually monitored very closely by the study investigators. For example, blood and urine samples may be collected regularly.

Other Phases of Clinical Trials

There are three phases of clinical trials that must be completed before a drug is approved by the Food and Drug Administration (FDA).

Clinical trial phases:

  • If a treatment appears safe at the end of a phase 1 clinical trial, it may move forward to a phase 2 clinical trial.
  • A phase 2 clinical trial is done to see if a treatment is effective. If a drug or treatment is deemed safe in a phase 1 trial and effective in a phase 2 trial, it will then enter a phase 3 clinical trial.
  • Phase 3 clinical trials often have a larger study population and are done to see if a treatment works better or has fewer side effects than available treatments.

Considering a Phase 1 Clinical Trial

There are a few reasons someone may consider participating in a phase 1 clinical trial. One is to have access to a new drug or procedure that has not yet been tested on humans and may offer you better benefits than available treatments. Another is the hope of improving medical care in a way that may help others with the same disease in the future.

That said, clinical trials are not for everyone.

Risks and Benefits

It's important to consider all of the risks and benefits of clinical trials if you are considering participating in one of these studies.

  • If you use a treatment that hasn't been widely used for your condition, you could expose yourself to potentially serious side effects and run the risk of having a worse outcome than you might have had otherwise.
  • And if the treatment turns out to be safe and effective, you could benefit from a better quality of life and/or longer survival.

Sometimes you might have certain characteristics that could make you more or less likely to experience benefits or side effects (these may include your age, genetic predisposition, or other factors) of the new treatment. But there can be many unknowns with new treatments, so the facts about these issues might not have been discovered yet.

It's often helpful to write down both the pros and cons of the study on a sheet of paper so you can weigh your options. There is not a right or wrong choice, only the choice that is best for you.

Other Options for Receiving Experimental Drugs

For the most part, the most common way for you to get access to an experimental treatment is to take part in a clinical trial.

Additionally, some people may qualify for compassionate use or expanded access to drugs that are not approved by the FDA. If you do not qualify for a clinical trial but an investigational treatment appears promising for your particular disease, you may qualify for compassionate drug use.

A Word From Verywell

Phase 1 clinical trials are the first medical studies in which a new or newly improved treatment is tested in humans. These studies may be risky, but they can have benefits. There is no surefire way to predict whether your outcome will be better or worse when you enroll in phase 1 clinical trial. But you can discuss the option with your doctor, who will be able to advise you based on your medical condition and the biological mechanisms of the treatment that's being tested.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Food and Drug Administration. The FDA's drug review process: Ensuring drugs are safe and effective.

  2. MD Anderson Cancer Center. Phases of clinical trials.

  3. American Cancer Society. Compassionate drug use.

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."