What Is a Phase III Clinical Trial?

Clinical trials advance through four distinct phases. Phase I tests safety on a small group of volunteers. Phase II measures initial effectiveness on a larger cohort. Phase III is where the investigation truly scales. These studies involve large groups of patients with the specific disease the trial drug intends to impact, often across multiple medical centers and sometimes across multiple countries. The goal is to generate the evidence a regulatory body like the FDA needs to approve the drug for widespread use.

The NIDDK notes that Phase III clinical trials are typically multi-center and involve several hundred patients randomized to two or more treatments, one of which is usually a placebo. The aim is to provide evidence for support of, or a change in, health policy or standard of care.

The Current Digestive-Disorder Treatment Landscape

Despite tremendous progress, many patients with digestive disorders still struggle to find lasting relief. As one NYU Langone physician put it, current therapies don't necessarily work indefinitely and there is a therapeutic ceiling. Even with over fourteen advanced therapies now available for ulcerative colitis and Crohn's disease alone, a significant number of patients fail to achieve durable remission.

This gap is precisely why Phase III trials matter. New drug classes are being explored at an unprecedented pace. Recent Phase II and III trials have evaluated novel S1P modulators like ozanimod and etrasimod, as well as IL-23 inhibitors such as risankizumab, mirikizumab, guselkumab, and brasikumab for their ability to induce and maintain remission in IBD. Results have been encouraging—for instance, the Phase III VIVID-1 study showed that 53 percent of patients on mirikizumab achieved clinical remission at one year, compared with 36 percent on placebo.

Beyond IBD, Phase III investigations are also active for gastroparesis, functional dyspepsia, celiac disease, and irritable bowel syndrome with diarrhea (IBS-D), broadening the scope of conditions that may benefit from next-generation therapies.

Seven Compelling Reasons to Participate

1. Access Treatments Before They Reach the Market

One of the most direct benefits is early access. Participating in a GI research trial allows patients to access brand-new treatment options that are not yet available to the public. For people who have exhausted standard therapies, this can be a lifeline.

2. Receive Highly Personalized, Frequent Medical Care

Trial participants are monitored far more closely than in routine clinical settings. Research centers offer clinical trial participants personalized care, cutting-edge medications, and highly individualized treatment at no cost, often resulting in more frequent and individualized care than is obtainable elsewhere. You receive regular check-ups, lab work, and specialist oversight throughout the study.

3. Contribute to Scientific Breakthroughs

Participation in clinical studies is an important way to learn more about GI illnesses and help find better treatment options. Many of the standard treatments patients receive today were developed based on the results of previous clinical trials. Your involvement directly shapes the future standard of care for millions of people worldwide.

4. Zero Out-of-Pocket Costs for Study-Related Care

Phase III trials almost always cover the costs of study medications, lab tests, imaging, and physician visits associated with the research protocol. GI Alliance reports that patients can participate in most clinical trials at zero cost.

5. Help Ensure Treatments Work Across Diverse Populations

For new treatments to serve everyone, clinical trials need participants of all races, ages, and sexes in order to collect data that has a wide range of applicability. By enrolling, you help researchers understand how a therapy performs across different demographic groups—a critical factor for FDA approval.

6. Gain a Deeper Understanding of Your Own Condition

Enrolling in a clinical trial enables participants to take an active role in their own health care, gain entrance to new research, and contribute to medical science. The detailed screening, monitoring, and follow-up inherent in a trial often reveal insights about your disease that routine visits might miss.

7. Help Close the Gap Where Current Therapies Fall Short

A leading gastroenterologist summarized the challenge succinctly: all available drugs work about half the time, and there has been no real game-changer. Each new participant in a Phase III trial brings the medical community one step closer to a therapy that could finally change that calculus.

Real-World Phase III Trials Recruiting Now

The following examples illustrate the breadth of Phase III gastroenterology research currently underway:

These trials represent just a fraction of the research landscape. NIDDK-supported programs cover conditions ranging from Helicobacter pylori infection to celiac disease to intestinal failure and short gut syndrome.

Who Qualifies? Understanding Eligibility Criteria

Eligibility varies by study but generally follows predictable patterns:

• Confirmed diagnosis: You will need documentation of your digestive disorder, often including endoscopy or imaging results within the past year.
• Treatment history: Many Phase III trials specifically seek patients who have had an inadequate response, loss of response, or intolerance to standard therapies such as corticosteroids, immunosuppressants, or biologic agents.
• Age and health status: Some studies recruit adults only; others focus on pediatric populations. Co-existing conditions may affect eligibility.
• Common exclusions: Active infections, pregnancy or intent to become pregnant, certain surgical histories (e.g., prior pyloroplasty), and significant liver injury are frequent exclusion criteria.

Candidates for GI clinical studies may include those with a treatment-resistant gastrointestinal disorder. Some studies also recruit healthy volunteers, particularly for observational or prevention-focused research.

What to Expect as a Participant

1. Screening: The study staff will thoroughly screen you to ensure qualification. This may involve blood work, imaging, endoscopy review, and a detailed medical history.
2. Informed consent: You will be asked to sign an informed consent form that outlines the study's purpose, procedures, risks, and your rights as a participant.
3. Baseline visit: Initial evaluations establish your starting health metrics.
4. Ongoing visits: Throughout the course of the trial, you return to the research facility regularly to undergo tests or evaluations. Many programs now offer a combination of in-person and telehealth visits, making participation more accessible.
5. Open communication: You should always report any concerns to the research staff. Ethical oversight committees (Institutional Review Boards) continuously monitor participant safety.
6. Completion or extension: Some studies offer long-term extensions. For example, certain UC trials allow participants who complete a 52-week treatment period to continue for up to four additional years.

Potential Risks and How They Are Managed

No medical intervention is without risk. Key considerations include:

• Side effects: Investigational drugs may have unknown or uncommon adverse effects. Phase III trials have already passed earlier safety hurdles, but close monitoring is still essential.
• Placebo assignment: In placebo-controlled trials, you may receive a placebo rather than the active drug. However, researchers monitor your condition closely, and rescue therapies or protocol adjustments are available if your symptoms worsen significantly.
• Time commitment: Regular clinic visits, lab draws, and symptom diaries require dedication. Modern trial designs increasingly incorporate telehealth to reduce burden.
• Emotional uncertainty: Not knowing whether you are receiving the active treatment can be stressful. Support from the research team and patient advocacy organizations can help.

Every Phase III trial is supervised by an independent Data Safety Monitoring Board that reviews outcomes at regular intervals and can halt a study if safety concerns emerge.

Key Takeaways

• Phase III trials are the gateway between promising science and FDA-approved treatments for digestive disorders.
• Participants gain early access to investigational therapies, receive intensive specialist care, and face zero study-related costs.
• Current trials span IBD, gastroparesis, IBS-D, celiac disease, and more—covering both adult and pediatric populations.
• Despite existing therapies, many GI patients do not achieve lasting remission, making new research participation critically important.
• Eligibility requirements are specific but transparent; your gastroenterologist can help determine whether a trial is right for you.
• Safety is rigorously monitored through informed consent, IRB oversight, and independent data safety committees.

Frequently Asked Questions

Is joining a Phase III clinical trial for a digestive disorder safe?

Phase III trials have already undergone Phase I and Phase II testing for safety and preliminary efficacy. Additionally, every trial is overseen by Institutional Review Boards and independent Data Safety Monitoring Boards that can pause or stop the study if risks outweigh benefits. While no treatment is entirely risk-free, the safeguards in place make Phase III participation one of the most closely monitored healthcare experiences available.

Will I have to pay anything to participate?

In the vast majority of Phase III GI trials, all study-related care—including the investigational medication, lab work, imaging, and specialist visits—is provided at no cost to participants. Some programs even reimburse travel expenses.

What digestive conditions are currently being studied in Phase III trials?

A wide range. Active trials are investigating treatments for Crohn's disease, ulcerative colitis, gastroparesis, IBS with diarrhea, GERD, celiac disease, intestinal failure, and short gut syndrome, among others. Both adult and pediatric populations are represented.

What happens if I am assigned to the placebo group?

Being randomized to placebo does not mean you receive no care. You still benefit from the intensive monitoring and specialist oversight built into the trial. If your condition worsens, protocols typically include rescue therapy provisions. Many modern trials also use active-comparator designs rather than pure placebos.

Can I leave a clinical trial once I have enrolled?

Yes. Participation in any clinical trial is entirely voluntary. You may withdraw at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.

How do I find a Phase III digestive-disorder trial near me?

Start by speaking with your gastroenterologist. You can also search ClinicalTrials.gov, the IFFGD clinical trial listings, or the GI Alliance research page. Many academic medical centers—including Stanford, Johns Hopkins, and UCSF—maintain searchable trial databases specific to gastroenterology.