Obesity (BMI ≥30): Finding the Right Clinical Trial

Why Clinical Trials Matter for Obesity Treatment

Obesity is a chronic, relapsing metabolic disease. The Endocrine Society's 2023 Clinical Practice Guideline formally classifies it as such and calls for long-term, individualized pharmacotherapy in eligible patients [1]. Yet only a fraction of qualifying adults currently receive any FDA-approved medication, and the pipeline of new agents is the most active it has been in decades.

Joining a clinical trial gives you two things standard care rarely offers: access to investigational therapies before FDA approval, and granular metabolic monitoring that most outpatient practices cannot provide.

The Scale of the Problem and the Pipeline

Obesity affects 41.9% of U.S. Adults, according to the CDC's most recent National Health and Nutrition Examination Survey data [2]. The direct medical cost attributable to obesity is estimated at $172.74 billion annually [3]. Despite that burden, the armamentarium of approved agents remained thin until 2021, when semaglutide 2.4 mg (Wegovy) became the first drug in nearly a decade to receive FDA approval for chronic weight management [4].

Since then, tirzepatide (Zepbound) was approved in November 2023, and at least six additional agents are in active Phase II or Phase III development, including retatrutide (a triple GIP/GLP-1/glucagon agonist), CagriSema (a combination of cagrilintide and semaglutide), and orforglipron (an oral GLP-1 receptor agonist) [5].

What Participants Actually Receive

Participants in Phase II and Phase III obesity trials typically receive the study drug at no cost, all protocol-mandated laboratory work, body composition imaging (often DEXA), and frequent structured visits with a multidisciplinary team. Some trials also provide dietary counseling, behavioral coaching, and transportation reimbursement. The National Institutes of Health's ClinicalTrials.gov record for each study lists compensation details under the "Contacts and Locations" tab.

Understanding Eligibility: The BMI Threshold and Comorbidity Rule

The FDA's guidance on anti-obesity medications sets two parallel eligibility tracks. The first track requires a BMI of 30 or above. The second allows enrollment at a BMI of 27 or above if the patient carries at least one weight-related comorbidity, including type 2 diabetes, hypertension, dyslipidemia, or obstructive sleep apnea [4]. Clinical trials frequently mirror this regulatory framework in their inclusion criteria.

Common Inclusion Criteria Across Major Trials

Across the STEP, SURMOUNT, and OASIS trial programs, the following inclusion criteria appeared consistently [6][7][8]:

• BMI ≥30 kg/m², or BMI ≥27 kg/m² with at least one qualifying comorbidity
• Age 18 to 75 years (some trials extend to age 80)
• Stable body weight, defined as <5 kg change in the 90 days before screening
• No prior bariatric surgery within 12 months, or no prior surgery at all in some protocols
• Willingness to use contraception if of childbearing potential, given the teratogenic risk signals seen with GLP-1 agonists in animal studies

Common Exclusion Criteria to Check Before Applying

Exclusion criteria vary by sponsor and phase, but the most frequent disqualifiers are:

• Current or recent use (<3 months) of any approved GLP-1 or GIP/GLP-1 agonist
• Personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 (a class-wide GLP-1 precaution)
• Severe renal impairment, defined as eGFR <30 mL/min/1.73 m² in most protocols
• Recent cardiovascular event (<6 months): myocardial infarction, stroke, or hospitalization for unstable angina
• Active malignancy or use of systemic immunosuppressants

Checking these against your own history before contacting a site saves time for both you and the research coordinator.

The Major Active Trial Programs: What Is Currently Enrolling

SURMOUNT and Tirzepatide Extensions

The SURMOUNT program established tirzepatide's efficacy. SURMOUNT-1 (N=2,539) showed that tirzepatide 15 mg produced a mean weight reduction of 20.9% at 72 weeks, compared with 3.1% for placebo (P<0.001) [7]. SURMOUNT-2 confirmed these findings in participants with type 2 diabetes [9]. Extension and combination studies are now enrolling through 2026, including SURMOUNT-5, which directly compares tirzepatide to semaglutide 2.4 mg head-to-head for the first time.

REDEFINE and Retatrutide

Retatrutide is a triple agonist acting on GIP, GLP-1, and glucagon receptors simultaneously. Phase II data published in the New England Journal of Medicine (N=338) showed that retatrutide 12 mg produced 17.5% weight loss at 24 weeks, a rate not previously seen at the midpoint of a trial [10]. Phase III (REDEFINE-1 and REDEFINE-2) is currently enrolling adults with BMI ≥30, or ≥27 with comorbidities, at sites across North America and Europe.

OASIS and Oral Semaglutide

OASIS-1 tested oral semaglutide 50 mg once daily in adults without diabetes (N=667). At 68 weeks, participants lost a mean of 15.1% of body weight vs. 2.4% with placebo [8]. This result matters because it suggests that injectable delivery is not required for clinically meaningful weight loss with a GLP-1 agonist, opening the door for patients with needle phobia or logistical barriers to injectables.

CagriSema Trials

CagriSema pairs the amylin analogue cagrilintide with semaglutide 2.4 mg. Early Phase II data presented at the 2023 European Congress on Obesity suggested mean weight loss of approximately 15.6% at 32 weeks from a relatively modest dose, with a favorable tolerability profile [11]. Phase III trials for this combination began enrolling in late 2024.

Behavioral and Device Trials

Not every trial tests a drug. The NIH-funded TREAT trial is examining whether structured time-restricted eating added to standard care improves weight outcomes beyond medication alone. Device trials for endoscopic gastroplasty, intragastric balloons, and vagal nerve blockade are also registered and open. Participants who prefer non-pharmacological approaches should filter ClinicalTrials.gov by "Intervention Type: Device" or "Behavioral."

How to Search ClinicalTrials.gov Effectively

ClinicalTrials.gov hosts more than 460,000 registered studies. Without the right filters, results are overwhelming. The following search sequence consistently surfaces relevant obesity trials [12].

Step 1: Use the Condition Field First

Type "obesity" or "overweight" into the Condition or Disease field, not the keyword field. The condition field maps to MeSH terms and returns more complete results.

Step 2: Apply Status and Phase Filters

• Status: "Recruiting" (not "Not Yet Recruiting" unless you want to plan ahead)
• Phase: "Phase 2" and "Phase 3" for drug trials with the most near-term access to new agents
• Age: Set to your age group to pre-filter eligibility

Step 3: Set a Proximity Filter

Use the "Distance from Location" field with your ZIP code and a 100-mile radius as a starting point. For rare or highly novel agents, expanding to 250 miles or considering telehealth-eligible studies is reasonable.

Step 4: Read the Full Protocol Document

Every ClinicalTrials.gov record has a "Study Documents" tab that may include the full protocol or a lay-language summary. Reading the eligibility criteria section before calling saves a 30-minute screening call.

Step 5: Contact Multiple Sites Simultaneously

Most Phase III obesity trials run at 50 to 200 sites. Contacting three or four simultaneously, rather than sequentially, can reduce your wait time from several months to days or weeks. Site coordinators are listed under "Contacts and Locations" with direct phone numbers and email addresses.

Evaluating Trial Quality and Safety Before You Enroll

Not all registered trials are equal. The following indicators separate well-designed studies from poorly resourced ones.

IRB Approval and Data Safety Monitoring Board

Every Phase II and Phase III trial involving an unapproved drug must have an active Institutional Review Board approval and an independent Data Safety Monitoring Board (DSMB). The DSMB reviews unblinded interim data and can stop the trial early for harm. The ClinicalTrials.gov record lists the oversight authority under "Oversight and Monitoring."

Primary Endpoint Specificity

Trials with a clearly stated primary endpoint, such as percent change in body weight from baseline at 68 weeks, are more rigorous than those listing composite or vague endpoints. Secondary endpoints should include cardiometabolic markers: waist circumference, fasting glucose, HbA1c, lipids, and blood pressure.

Sponsor Reputation and Phase

Sponsor-funded Phase III trials by companies with prior FDA approvals in metabolic disease carry lower operational risk of early termination than small investigator-initiated Phase II studies. Academic Phase II trials often access the most novel mechanisms first.

Published Safety Data From Earlier Phases

Before enrolling in a trial for any new agent, search PubMed for Phase I and II safety publications. For retatrutide, for example, Phase II data published in the NEJM provide detailed adverse-event tables showing that nausea (45%), vomiting (20%), and diarrhea (27%) were the most common side effects at the 12 mg dose, consistent with the class profile [10].

Matching Your Comorbidity Profile to the Right Trial

Type 2 Diabetes

If you have type 2 diabetes and a BMI ≥27, SURMOUNT-2, the SCALE Diabetes extension, and several oral GLP-1 trials have arms specifically designed for this population. The American Diabetes Association's 2024 Standards of Care recommend GLP-1 receptor agonists as preferred agents for weight management in adults with type 2 diabetes and obesity [13]. Enrolling in a diabetes-specific obesity trial often means you can remain on your current diabetes regimen while receiving the investigational weight-loss therapy.

Cardiovascular Disease

The SELECT trial (N=17,604) demonstrated that semaglutide 2.4 mg reduced major adverse cardiovascular events by 20% in adults with pre-existing cardiovascular disease and overweight or obesity (without diabetes) [14]. This finding has prompted several cardiovascular outcomes trials for next-generation agents. If you have established cardiovascular disease, specifically look for trials with a MACE endpoint or a cardiovascular substudy, as these often include closer cardiac monitoring.

Sleep Apnea

The SURMOUNT-OSA trial evaluated tirzepatide in patients with obesity-related obstructive sleep apnea. Results published in the NEJM (2024) showed that tirzepatide reduced the apnea-hypopnea index by approximately 29 events per hour vs. 5.5 events per hour for placebo in patients not using PAP therapy [15]. Sleep apnea-focused trials may include home sleep testing and polysomnography as protocol procedures.

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Semaglutide 2.4 mg is under active Phase III evaluation for MASLD (formerly NAFLD/NASH) in the ESSENCE trial. MASLD affects roughly 25% of the global population and is strongly associated with obesity [16]. If you have biopsy-confirmed or imaging-diagnosed MASLD, trials focused on this overlap may offer both weight reduction and hepatic benefit.

Regulatory and Ethical Protections for Trial Participants

The FDA regulates all Phase I through Phase III trials under 21 CFR Parts 312 (Investigational New Drug) and 50 (Informed Consent). Every participant must sign an informed consent document before any study procedures begin. The document must describe the study purpose, all known risks, alternatives to participation, and your right to withdraw at any time without penalty [17].

The Endocrine Society's position statement on obesity pharmacotherapy states: "Patients should be fully informed of the investigational nature of study medications and the possibility that they may receive placebo." Placebo arms in obesity trials almost universally include a structured lifestyle intervention component, so no participant receives no treatment at all.

Randomized controlled trials in obesity generally use a 2:1 or 3:1 active-to-placebo allocation, meaning your probability of receiving the active drug is 67% to 75% in most Phase III designs. Open-label extension phases following the blinded period typically offer all participants the active drug.

Practical Steps After You Identify a Promising Trial

Gather Your Records

Site coordinators will ask for your most recent BMI measurement, fasting labs (glucose, HbA1c, lipid panel, comprehensive metabolic panel), medication list, and a brief medical history. Having these available at the first call compresses the pre-screening process from weeks to days.

Ask the Right Questions

Before agreeing to a screening visit, ask the site coordinator:

1. What is the allocation ratio for active drug vs. Placebo?
2. Is there an open-label extension phase after the blinded period?
3. What happens to my current medications during the trial?
4. Is there a run-in period, and does it involve a placebo or caloric restriction?
5. How many site visits are required, and can any assessments be done via telemedicine?

Understand the Off-Trial Plan

Investigational drugs are not available outside the trial once you withdraw or once the study ends, unless the drug has been approved. Ask the site team about their standard-of-care plan if you lose access to the study drug. Some sponsors offer compassionate-use or expanded-access programs; these are also registered on ClinicalTrials.gov under "Expanded Access."

Summary Table: Selected Active Obesity Trials (2024 to 2026)

| Trial | Drug / Intervention | Phase | Primary Endpoint | Estimated Completion | |---|---|---|---|---| | SURMOUNT-5 | Tirzepatide vs. Semaglutide | III | % body weight change at 72 weeks | 2025 | | REDEFINE-1 | Retatrutide 12 mg | III | % body weight change at 48 weeks | 2026 | | CagriSema Phase III | Cagrilintide + semaglutide | III | % body weight change at 68 weeks | 2026 | | OASIS Extension | Oral semaglutide 50 mg | III | Sustained weight loss at 104 weeks | 2025 | | SELECT Extension | Semaglutide 2.4 mg (CV outcomes) | III | MACE at median 4-year follow-up | 2025 | | ESSENCE | Semaglutide 2.4 mg (MASLD) | III | MASLD resolution at 72 weeks | 2025 |