How Long Do Clinical Trials Last? Duration of Clinical Trials

How long do clinical trials last? This Clinical Trial Guide article explains the duration of clinical trials.
Back January 25, 2023

This Clinical Trial Guide article explains the duration of clinical trials and answers the question: How long do clinical trials last? Three main phases are conducted in clinical trials, with the fourth and final phase taking place upon the approval from the US Food and Drug Administration (FDA) for the new drug or treatment to be used on a large number of patients who have the condition.
Below, we outline the time that each phase can generally take according to the FDA.

Phase I:

Purpose: This phase studies a small number of mostly healthy volunteers to monitor for side effects, safety, and dosage. Approximately 70% of drugs advance to phase II.

Duration: Phase I takes several months to complete due to the diligent research being executed as researchers gather data on how the new drug or treatment interacts with the human body. Only time reveals these results, and researchers can adjust dosing measures based on the recorded data from animal testing in order to discover side effects and how much the human body can tolerate of the new drug. Upon approval to advance, phase II will commence.

Phase II:

Purpose: Phase II studies several hundred people that have the disease or condition for further monitoring and collecting data. Approximately 33% of drugs advance to phase III.

Duration: As the number of participants increases, so does the duration of the phase—generally, this takes anywhere from several months to two years to complete. Because participants are not completely healthy, adding a new variable into the mix when studying if the new treatment is effective takes time. These studies aren’t large enough to be able to fully conclude if the drug will be beneficial or not, but they do provide researchers with additional safety and side effects data when transitioning into phase III research protocols.

Phase III:

Purpose: This phase studies several hundred to several thousand volunteers with the disease or condition, studying effectiveness and monitoring for adverse reactions. Approximately 25-30% of these drugs advance to Phase IV.

Duration: If a drug advances to phase III, the studies conducted are to demonstrate whether the product offers treatment benefits to a more specific population group. This phase can last from one to four years on average. Due to the length of time and large number of study participants, the results are more likely to reveal more long-term side effects or even some rare side-effects.

Phase IV:

Purpose: This phase involves several thousands of participants with the disease or condition and is the final phase for monitoring safety and efficiency in a large study group.

Duration: Phase IV only takes place after the FDA approves the new treatment or drug during the Post-Market Safety Monitoring and will continue to be researched and monitored during the duration of its practice.

These four phases each play a very distinct role and therefore, the time frame on each phase varies. The next phase cannot start until the new treatment or drug gets approved to advance. [Image – Clinical Trial Phase Duration]


With that said, how long the trial will last altogether is not to be confused with how long the trial will go on for the volunteered participant. The length for a participant in a clinical trial will truly depend on which phase (I-IV) of the extensive study they join. If a clinical trial is makes it all the way to approval from beginning to end (this happens with an average of less than 12% of clinical trial medicines), it can take an average of six to seven years.

This doesn’t include the time that it takes to find participants for a clinical trial. According to the Pharmaceutical Research and Manufacturers of America (PhRMA), “it can take months or even years to recruit and enroll volunteers to participate in studies” (Biopharmaceutical Research & Development). Clinical trials have always been a lengthy process, but it is necessary for the safety and study of medicines developed to combat disease in the complexity of the human body.

Therefore, when considering partaking in a clinical trial study, be sure to ask questions in the interview such as…
  • What phase of the study am I joining?
  • How long is it expected to last from when I join?
  • Would I be likely to proceed to the following phase?

Always remember that if you become accepted as a study participant, you are allowed to discontinue at any point during the trial.

Back to The Guide

Back to Home Page

Clinical Trials

Power your next Clinical Trial

Connect and see if your trial fits for our site package and promotion!