Obesity (BMI ≥30): Emerging Research and Trials to Watch

Why the Obesity Pipeline Matters Now

Obesity affects 42.4% of U.S. adults according to 2017-2020 NHANES data from the CDC. It is the primary driver of type 2 diabetes, cardiovascular disease, and at least 13 types of cancer. Until 2021, approved anti-obesity medications produced modest results (5% to 10% total body weight loss). Semaglutide 2.4 mg changed expectations: in STEP-1 (N=1,961), participants lost a mean of 14.9% body weight at 68 weeks versus 2.4% with placebo [1].

Tirzepatide raised the bar further. The SURMOUNT-1 trial (N=2,539) demonstrated 20.9% mean weight loss at the highest dose (15 mg) over 72 weeks [2]. These results proved that pharmacologically driven weight reductions above 15% are achievable at scale. The pipeline building on these proofs of concept now targets 25% or greater total body weight loss, lean mass preservation, and oral delivery.

The American Association of Clinical Endocrinology (AACE) 2023 obesity algorithm explicitly calls for a "complications-centric" treatment model, moving away from BMI alone as the decision point for therapy [3]. This reframing supports earlier, more aggressive pharmacotherapy, which makes the incoming wave of new agents clinically relevant for millions of patients who previously would not have been offered medication.

Retatrutide: The Triple-Hormone Agonist

Retatrutide activates three receptors at once: GLP-1, GIP, and glucagon. That third target, the glucagon receptor, increases energy expenditure and hepatic fat oxidation, effects that GLP-1/GIP dual agonists do not fully capture.

In the phase 2 trial (N=338) published in the New England Journal of Medicine, the highest dose of retatrutide (12 mg) produced 24.2% mean body weight loss at 48 weeks [4]. Weight loss curves had not plateaued at study end, suggesting further reductions with longer treatment. Gastrointestinal side effects (nausea, diarrhea, vomiting) were the most common adverse events, consistent with the incretin drug class, though rates appeared manageable at titrated doses.

Eli Lilly's phase 3 program (TRIUMPH) is now enrolling across multiple populations: adults with obesity, adults with obesity and type 2 diabetes, and those with obesity-related comorbidities. If phase 3 confirms the phase 2 signal, retatrutide could be the first approved triple agonist. The glucagon component may also offer liver-specific benefits. A secondary analysis showed reductions in liver fat exceeding those seen with tirzepatide [4].

Orforglipron: An Oral GLP-1 That Could Change Access

Injectable GLP-1 receptor agonists face supply constraints and patient adherence barriers tied to needle aversion. Orforglipron is a small-molecule, non-peptide oral GLP-1 receptor agonist. Because it is not a peptide, it does not require the absorption-enhancing formulation used by oral semaglutide (Rybelsus), and it can be taken without fasting restrictions.

Phase 2 data (N=272) published in the New England Journal of Medicine showed that orforglipron 45 mg daily led to 14.7% body weight loss at 36 weeks compared to 2.3% with placebo [5]. The side-effect profile was dominated by nausea and vomiting, which peaked during dose escalation and declined over time.

Amgen's phase 3 ATTAIN program is the key trial series. Results are expected in 2026. If approved, orforglipron would be the first oral non-peptide GLP-1 agonist for obesity, potentially reaching populations who refuse or cannot access injectables. That is a large group. A 2023 analysis found that fewer than 2% of eligible U.S. adults with obesity filled an anti-obesity medication prescription, and injection burden was cited as a top barrier [6].

"If we can deliver GLP-1-class efficacy in a once-daily pill without food restrictions, we remove one of the biggest practical obstacles to treatment uptake," said Dr. Sean Wharton, lead author of the orforglipron phase 2 trial [5].

Survodutide: GLP-1 Plus Glucagon for Metabolic Overlap

Survodutide is a dual GLP-1 and glucagon receptor agonist developed by Boehringer Ingelheim and Zealand Pharma. In the phase 2 trial (N=387), the 4.8 mg dose produced 18.7% weight loss at 46 weeks [7]. Like retatrutide, the glucagon component adds direct hepatic effects.

An early analysis of liver imaging biomarkers in participants with MASLD (metabolic dysfunction-associated steatotic liver disease) showed significant reductions in hepatic fat fraction. This positions survodutide as both an obesity and a liver disease candidate. The phase 3 SYNCHRONIZE program for obesity is underway, alongside the AURORA program focused specifically on MASH (metabolic dysfunction-associated steatohepatitis) with fibrosis. Results from SYNCHRONIZE-1 are anticipated in late 2026.

The dual agonist's thermogenic properties via glucagon receptor activation may lead to greater total energy expenditure than GLP-1-only agents, though head-to-head trials with semaglutide or tirzepatide have not been published. Gastrointestinal adverse events remain the dose-limiting factor. The phase 2 discontinuation rate due to adverse events was 5% at the highest dose [7].

CagriSema: Amylin Plus GLP-1

CagriSema combines cagrilintide, a long-acting amylin analogue, with semaglutide 2.4 mg in a single weekly injection. Amylin is a pancreatic hormone co-secreted with insulin that slows gastric emptying, suppresses glucagon, and acts on brainstem satiety centers through pathways partially distinct from GLP-1.

In the phase 2 trial (N=92), CagriSema produced 15.6% weight loss at 32 weeks [8]. This was numerically greater than semaglutide alone (5.1%) or cagrilintide alone (8.1%) in the same study, suggesting additive or synergistic effects.

Novo Nordisk's phase 3 REDEFINE program is large, with trials spanning obesity, obesity with type 2 diabetes, and obesity with established cardiovascular disease. The REDEFINE-1 topline results showed 22.7% mean weight loss with CagriSema at 68 weeks, versus 15.5% for semaglutide 2.4 mg alone and 1.2% for placebo [9]. This is the first phase 3 agent to outperform semaglutide 2.4 mg in a head-to-head comparison. FDA submission is expected in 2026.

"The amylin pathway offers complementary satiety signals. Combining it with GLP-1 receptor agonism appears to produce weight loss outcomes we could not achieve with either mechanism alone," stated Dr. Ildiko Lingvay, principal investigator on REDEFINE-1, as reported at the 2024 European Association for the Study of Diabetes (EASD) annual meeting.

Maridebart Cafraglutide (AMG 133): A Contrarian GIP Approach

Where tirzepatide activates both GLP-1 and GIP receptors, AMG 133 (maridebart cafraglutide, developed by Amgen) takes the opposite approach to GIP. It is a bispecific molecule that agonizes GLP-1 while antagonizing (blocking) GIP.

Phase 2 data showed up to 14.5% weight loss at just 12 weeks with monthly dosing [10]. The rapid onset and monthly injection schedule distinguish this agent from weekly competitors. GIP receptor antagonism may reduce adipose tissue lipid storage through a mechanism distinct from GIP agonism, though the underlying biology of GIP in obesity remains debated. Some researchers hypothesize that both GIP activation and GIP blockade can produce weight loss through different downstream pathways.

Phase 3 trials are planned. The monthly dosing interval is clinically attractive for long-term adherence, given that most competing agents require weekly injections.

Bimagrumab: Preserving Muscle During Weight Loss

A known limitation of all current anti-obesity pharmacotherapies is lean mass loss. Roughly 25% to 40% of weight lost with GLP-1 receptor agonists consists of lean tissue, including skeletal muscle [11]. This is especially concerning in older adults, where sarcopenic obesity worsens functional outcomes.

Bimagrumab is a fully human monoclonal antibody that blocks activin type II receptors, which regulate muscle growth through the myostatin/activin signaling pathway. In a phase 2 trial in adults with type 2 diabetes and obesity (N=75), bimagrumab produced a unique body composition shift: fat mass decreased by 20.5% while lean mass increased by 3.6% at 48 weeks, compared to fat mass loss of 0.5% with placebo [12]. Published in JAMA Network Open, these results suggest bimagrumab could be combined with GLP-1-based therapies to preserve or build muscle while maximizing fat loss.

Versanis Bio (acquired by Eli Lilly) is advancing bimagrumab into larger trials as a potential combination partner for tirzepatide or retatrutide. No phase 3 obesity data are available yet, but the muscle-sparing mechanism addresses one of the most frequently cited clinical concerns about the current generation of weight loss drugs.

Pemvidutide and the Liver-Obesity Nexus

Pemvidutide, developed by Altimmune, is another GLP-1/glucagon dual receptor agonist with a specific focus on MASLD/MASH. Phase 2 data (MOMENTUM trial, N=391) showed 15.6% weight loss at 48 weeks alongside a 78% mean relative reduction in liver fat measured by MRI-PDFF, with 82% of participants achieving at least a 30% reduction [13].

This overlap between obesity and liver disease trials reflects a clinical reality: roughly 30% of adults with obesity have MASLD [14]. Agents that address both weight and hepatic fat deposition could simplify treatment for a condition that currently has only one FDA-approved drug (resmetirom, for MASH with fibrosis). The phase 2b IMPACT trial for MASH is ongoing.

Gene-Based and Experimental Approaches on the Horizon

Beyond incretin-based pharmacotherapy, several mechanistically novel approaches are in early stages:

Leptin sensitizers. Leptin resistance is a hallmark of obesity, but direct leptin replacement has failed in non-deficient populations. New small molecules targeting the leptin receptor signaling pathway (JAK2-STAT3) are in preclinical development [15].

GDF15 analogues. Growth differentiation factor 15 (GDF15) signals through the GFRAL receptor in the brainstem to suppress appetite. Several pharmaceutical companies have GDF15-based molecules in phase 1 trials.

CRISPR-based interventions. Preclinical animal models have demonstrated that editing the MC4R pathway (which controls energy balance) can reverse obesity phenotypes. Human translation is years away, but the possibility of a one-time genetic correction for monogenic obesity forms (which affect roughly 5% to 10% of severe obesity cases) is under active investigation [16].

Microbiome-targeted therapies. The gut microbiome influences energy harvest, bile acid metabolism, and incretin secretion. Clinical trials of engineered microbes and defined bacterial consortia for obesity are in phase 1/2, though effect sizes have been small so far compared to pharmacological agents.

How Current Guidelines Frame These Advances

The 2023 AACE Consensus Statement recommends that clinicians choose anti-obesity medications based on a complications-centric model, selecting agents that address the specific comorbidities present in each patient rather than targeting BMI alone [3]. The Endocrine Society 2024 clinical practice guideline formally recommends GLP-1 receptor agonists as first-line pharmacotherapy for adults with BMI ≥30, and considers GLP-1/GIP dual agonists where available.

The ADA Standards of Care 2024 designate semaglutide 2.4 mg and tirzepatide as preferred agents for patients with obesity and type 2 diabetes, citing their dual metabolic benefits [17]. As pipeline agents demonstrate weight loss above 20%, the question for guidelines shifts from whether to treat obesity pharmacologically to which combination or sequence of agents is optimal for a given patient profile.

The USPSTF continues to recommend that clinicians offer or refer adults with BMI ≥30 to intensive behavioral interventions. The task force has not yet issued updated guidance incorporating the newer pharmacotherapy data, though a review is expected.

What Clinicians Should Watch For

Three milestones over the next 12 to 18 months will shape obesity treatment:

First, the REDEFINE program's full phase 3 readout for CagriSema will establish whether amylin-GLP-1 combinations become a new efficacy benchmark. Second, orforglipron's phase 3 ATTAIN results will determine if oral delivery can match injectable efficacy. Third, retatrutide's TRIUMPH program will test whether triple agonism delivers on the 24% weight loss signal seen in phase 2. Each of these, if positive, will likely prompt guideline revisions and payer coverage reassessments.

Clinicians treating patients with BMI ≥30 should discuss the evolving pipeline openly. Patients who discontinued prior pharmacotherapy due to side effects or inadequate response may be candidates for next-generation agents once approved. For patients already responding well to semaglutide or tirzepatide, these emerging options represent potential step-up therapies if weight loss plateaus or if lean mass preservation becomes a priority.

Monitoring hepatic, cardiovascular, and metabolic endpoints across these trials will help clarify whether specific agents offer advantages for subpopulations with MASLD, heart failure with preserved ejection fraction, or chronic kidney disease, all of which are being studied in dedicated arms of the major phase 3 programs.