Unraveling clinical trial timelines: How long does each phase take?

The overall drug development timeline, spanning from discovery through to licensing, can be 15 years or longer. There are many steps and clinical phases involved, some of which take longer than others. In this article, we will focus on clinical trials, during which a drug or treatment has to go through different clinical trial phases to assess its safety and effectiveness in humans. There is enormous variability in the timelines of clinical trial phases, so in general, we can answer the question as follows:

Q: How long do clinical trials take?

A: It depends!

The actual timeline of any clinical trial depends on multiple factors, some of which include:

  • The type of drug or treatment being tested
  • Type and phase of trial
  • Number of treatments and data required
  • Clinical trial recruitment process
  • Patient retention
  • Regulatory requirements

Overview of the drug development timeline

Generally speaking, it takes a long time for a drug to go through the different stages and phases of clinical research. Development of most new drugs, from discovery to marketing approval, usually takes between 10 and 15 years, although this figure can vary widely.

Recent industry trends actually indicate that trial phases are increasing in duration, in part due to the increasing customization and complexity of trials involving new technologies such as electronic data capture (EDC) methods, at-home measurements involving wearable devices, and the organizational requirements of managing decentralized and hybrid trials [1].

The general pipeline a drug goes through during the drug development and clinical research process is as follows:

1. Discovery and development

2. Pre-clinical research

3. Investigational New Drug (IND) application

4. Clinical trials

  • Phase 0 (optional)
  • Phase I
  • Phase II
  • Phase III

5.New Drug Application (NDA) submission for FDA approval

6. Phase IV

How long do clinical trials take? Phase lengths and other factors impacting timeline

Each trial has its own unique design and protocol, with some being more complicated than others, which is why clinical trial lengths vary. So, while we can say the average is between 10-15 years, there is no simple answer to this question. Let’s take a quick look at how long the different phases take as well as some of the main factors that dictate clinical trial timelines.

Clinical trial phases

In general, the length of each phase increases as the trial progresses. There are four different clinical trial phases, which all serve different purposes. The timelines of each phase presented here are approximate and are only generalizations.

1. Phase I trials

Phase I trials usually last from one to four months. Researchers introduce the drug to humans for the first time (usually healthy volunteers) and look at pharmacodynamics and how well it is tolerated.

2. Phase II trials

Phase II trials tend to last anywhere from several months to two years. Researchers determine the optimal dosage, assess the effects of the treatment on the condition it’s designed to treat, and collect more information about tolerance and side effects.

3. Phase III trials (Pivotal trials)

Phase III trials can last for several years as researchers gather data about how well the novel drug works compared to standard therapies, in a larger number of participants with the condition being targeted. These studies are the last clinical phase before submitting the drug for FDA approval with a new drug application (NDA).

4. Phase IV trials (Post-marketing surveillance studies)

Phase IV studies, or post-marketing studies, are long term studies of the performance of the drug in real-world use. Phase IV studies can last for multiple years depending on the specific questions the researchers want to answer, and are usually designed to assess side effects of long-term use, economic costs of the treatment, quality of life for those taking the drug, and other similar questions about health outcomes.

Clinical trial design and regulatory approval

The design and regulatory approval for clinical trials is another factor impacting timelines. All clinical trials require their own unique design and protocol to answer the research hypotheses and collect the appropriate data, from the appropriate pool of participants. Further, every single part of the clinical trial, from advertising, marketing, and creative content to the protocol itself needs to pass approval by an institutional review board (IRB) or independent ethics committee (IEC). Thus, designing and refining the study protocol and all related materials, and then getting it all approved, represents a significant investment of time. The process may not be linear, either, as anything that is not approved will have to be re-designed and pass a new round of approval before the trial can begin.

Clinical trial recruitment

Clinical trial recruitment is often a long process in clinical trials, and also one which tends to cause delays. In fact, it was reported that 90% of clinical trials worldwide fail to meet enrollment timelines and are required to extend the recruitment timeframe to avoid having to cancel the study [2]. Although this is a multi-faceted problem, one key factor is patient accessibility, which is a double-sided problem; patients may not know about clinical trials or may have trouble finding clear information about how to find and participate in a trial, and researchers often lack ways to access eligible patients. Solutions like Power's patient recruitment marketplace help both investigators and patients by connecting patients directly with clinical trial sites.

The nature of the trial is a major factor in recruitment and enrollment, as trials researching a treatment for a rare disease have fewer potential participants than a trial enrolling healthy volunteers, for example. On the other hand, it may be easier to find high-eligibility participants with rare conditions if their cases are documented, and it can be hard to sift through overly large pools of potential participants when many of them may not even be interested in participating.

Clinical trial participation

If you are considering participating in a clinical trial, it is normal to have a lot of questions. One factor impacting your decision may be the timeline. It is important to speak with the investigators to clarify any doubts you may have and ensure you are completely comfortable with the number of study visits required, including any travel and time off work that those may imply, as well as the planned duration of the trial overall.


As we have seen, clinical trial timelines can vary significantly from study to study. The question “how long does a trial last” does not have a straight answer.

Regardless of the expected duration of a given trial, if you are considering participating, it is important to understand the details of the trial timeline so that you can make sure you are able to commit to the complete process in order to maximize the value of your participation as well as any potential benefits you may reap.


[1] https://www.centerwatch.com/articles/25033-trend-of-longer-trial-timelines-is-likely-to-continue

[2] https://www.ncbi.nlm.nih.gov/books/NBK50886/