How long do clinical trial phases take?

Before any new medication, treatment, or therapy can be administered to patients, it must progress through the proper clinical trial phases, which are designed to test the drug or device in question for safety and effectiveness. This process can take a long time — in most cases, an average of 10 years will pass between initial discovery to full approval, with the clinical trial stages taking six to seven years of that time.

Even before reaching the clinical trial stage, there are other types of medical research that go into discovering new therapies. All research begins in the discovery phase, which is the three to six years that involves investigating new ideas, followed by animal trials. After these two phases are done, a potential treatment is able to enter the first phase of clinical trials with human participants.

How long do clinical trial phases take?

Every clinical trial phase has a timeline on paper. Phase 1 takes months. Phase 3 takes years. None of those timelines include how long it takes to find, educate, and enroll the patients each phase depends on.

This guide covers how long each clinical trial phase takes, what each phase is designed to answer, and where clinical trial timelines most often slip, along with what sponsors can do about it.

Clinical trial phases at a glance

Source: U.S. Food and Drug Administration

What happens before a clinical trial begins?

Before any clinical trial can enroll its first participant, a potential treatment goes through discovery and development, followed by preclinical research in the lab and in animals. These early stages answer basic safety questions, but they can't show how a drug will interact with the human body.

Next, the sponsor submits an Investigational New Drug (IND) application to the FDA. It includes animal study and toxicity data, manufacturing information, and the clinical protocols for the planned studies. The FDA has 30 days to review the original IND submission before clinical research can begin.

The protocol is also where sponsors decide who qualifies to participate, how many people the study needs, and how long it will last. Those decisions shape every timeline that follows.

How long does each clinical trial phase take?

Phase 1: several months

Phase 1 clinical trials test a new drug's safety and find out how much of it the body can tolerate. They typically enroll 20 to 100 healthy volunteers or people with the condition. For cancer drugs, Phase 1 studies are conducted in patients who have that type of cancer. About 70% of drugs move on to Phase 2.

Phase 2: several months to two years

Phase 2 clinical trials give the drug to up to several hundred people with the condition it's being developed for. These studies aren't large enough to prove the drug is beneficial. Instead, they gather more safety data and help researchers design the Phase 3 protocol. About 33% of drugs move on to Phase 3.

Phase 3: one to four years

Phase 3 clinical trials, sometimes called pivotal studies, enroll 300 to 3,000 people and are designed to show whether the treatment offers a real benefit to a specific population. Because they're larger and longer, they provide most of the safety data and are more likely to surface rare or long-term side effects. About 25 to 30% of drugs move on to the next stage.

FDA review

After Phase 3, the sponsor submits a New Drug Application (NDA) or Biologics License Application (BLA) to the FDA. The FDA reviews the total evidence on the drug's safety and effectiveness before deciding whether to approve it.

Phase 4: after approval

Phase 4 clinical trials take place after FDA approval and involve several thousand people with the condition. They monitor the treatment's long-term safety and effectiveness in the wider patient population.

Why do clinical trial timelines slip?

The phase durations above assume something that often isn't true: that enough eligible patients will be ready to enroll when the clinical trial opens.

Clinical sites underperform. According to research from the Tufts Center for the Study of Drug Development, 11% of clinical trial sites fail to enroll a single patient. Every clinical site that underdelivers puts more pressure on the rest of the enrollment plan.

Eligibility criteria narrow the pool. Criteria that look reasonable on paper, such as a recent test result, a medication history, or a body mass index cutoff, can screen out a large share of the patients who were interested in taking part.

Unclear clinical trial information creates patient recruitment drop-off. Patients who understood clinical research were twice as likely to say they would participate in a clinical trial. (Antidote survey of nearly 4,000 patients). When patient-facing materials are unclear, willing and eligible patients screen themselves out before they ever reach a clinical site.

Referral-to-randomization takes time. It can take several weeks for a patient to move from an online screener to a phone call, a screening visit, consent, and randomization. If the patient recruitment plan doesn't account for that lag, each clinical site's monthly targets fall behind from the start. Our clinical trial recruitment rate calculator shows how to set realistic per-site targets.

How can sponsors protect their clinical trial timeline?

Plan patient recruitment before choosing clinical sites. Sites that are inconvenient for patients, or saturated with competing clinical trials, are harder to fill. Ask candidate clinical sites how they recruit patients and what their recent enrollment numbers look like.

Test eligibility criteria before the protocol is locked. Measuring how real patients respond to the draft criteria shows which requirements suppress enrollment while there's still time to adjust them.

Build patient education into patient recruitment. Patients who understand what a clinical trial involves are more likely to stay in the process, and in Antidote's patient survey, twice as likely to say they would take part. Plain-language materials reduce drop-off before the screening visit.

Pre-screen and respond quickly. Reaching interested patients while their intent is high, and confirming eligibility before referral, means clinical sites spend their time on patients who are likely to qualify.

How much time does a clinical trial take for participants?

Many clinical trials last several years but only require a few visits during that time. Participants are often asked to keep an online or paper journal between visits so the study team has accurate data at each check-in. The study team is the best resource for specific scheduling details.

Participants can withdraw from a clinical trial at any time, for any reason. Some clinical trials also end early if researchers aren't getting meaningful results.

Frequently asked questions

How long do clinical trial phases take in total?

According to the FDA, Phase 1 lasts several months, Phase 2 lasts several months to two years, and Phase 3 lasts one to four years. Including discovery, preclinical research, and regulatory review, PhRMA estimates that developing a new medicine takes an average of 10 to 15 years.

Which clinical trial phase takes the longest?

Phase 3 is typically the longest of the pre-approval phases, lasting one to four years and enrolling 300 to 3,000 participants. Phase 4 continues after approval.

What percentage of drugs make it through clinical trials?

According to PhRMA, only 12% of drugs that enter clinical trials are ultimately approved by the FDA.

Why do clinical trials get delayed?

Patient recruitment is a frequent cause. Tufts CSDD found that 11% of clinical trial sites fail to enroll a single patient, and restrictive eligibility criteria can shrink the qualified patient pool further.

Can participants leave a clinical trial early?

Yes. Participants can withdraw from a clinical trial at any time, for any reason.