New obesity drug mechanisms beyond GLP-1 agonists

Why GLP-1 monotherapy is no longer enough

GLP-1 receptor agonists like semaglutide achieve 10–15% weight loss — a genuine advance, but still well below the 25–35% reduction delivered by bariatric surgery. That therapeutic gap is the primary driver behind a wave of multi-receptor drug development targeting obesity and metabolic disease. The global obesity epidemic affects over 650 million adults worldwide, with type 2 diabetes mellitus closely intertwined in what researchers now call “diabesity,” making the stakes for better pharmacotherapy exceptionally high.

The rationale for multi-receptor targeting is rooted in biology. Body weight and glucose homeostasis are regulated by complex, redundant mechanisms. Single-target therapies face inherent limitations because compensatory physiological responses blunt their effects over time. Simultaneously activating complementary pathways can produce synergistic metabolic benefits that no single agonist can replicate. According to WHO, obesity is now a leading global health priority — and the pharmaceutical industry has responded with over 30 dual and triple agonist programs currently in clinical development.

The benchmark for success has also shifted. Bariatric surgery remains the gold standard for durable weight loss, and any pharmacological approach must close that gap to be considered a genuine alternative for patients who cannot or will not undergo surgery. The agents described in this article represent the most serious attempt yet to achieve that goal.

Dual GLP-1/GIP agonists: the tirzepatide breakthrough

Tirzepatide — an imbalanced GLP-1R/GIPR co-agonist developed by Eli Lilly and approved by the FDA in May 2022 — has already established that dual agonism is clinically superior to GLP-1 monotherapy, achieving 22.5% weight loss at 72 weeks in the SURMOUNT-1 trial at the 15 mg dose. That single data point reshaped industry expectations for what obesity pharmacotherapy can deliver.

GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 are both incretin hormones secreted after meals, but their combined pharmacological effects are more than additive. While GIP was initially thought to promote weight gain based on receptor knockout studies, pharmacological GIPR agonism at supraphysiological levels paradoxically enhances weight loss when combined with GLP-1R activation. Tirzepatide’s mechanism involves three interlocking actions: synergistic β-cell stimulation superior to either hormone alone; central appetite suppression through hypothalamic GIP signaling; and adipose tissue remodeling through GIPR-mediated lipolysis and fat oxidation.

The drug’s design is deliberately imbalanced — it favors GIPR potency approximately five-fold over GLP-1R — a choice engineered to maximize the therapeutic index by reducing nausea while preserving efficacy. Beyond weight loss, tirzepatide also demonstrated reduced major adverse cardiovascular events in high-risk populations, a benefit that positions it well beyond a simple weight-loss agent.

Dual GLP-1/glucagon agonists: leveraging thermogenesis

Dual GLP-1/glucagon receptor agonists take a different approach from the GIP-based strategy: they exploit glucagon’s ability to increase metabolic rate and thermogenesis, clear hepatic fat, and suppress appetite centrally — while using GLP-1 co-agonism to counteract glucagon’s hyperglycemic effects. The result is a drug class particularly well-suited to patients with metabolic-associated steatohepatitis (MASH) and those where enhanced energy expenditure is a treatment priority.

Glucagon was traditionally viewed only as a counter-regulatory hormone that raises blood glucose. But at pharmacological doses combined with GLP-1R activation, it promotes lipolysis and reduces hepatic steatosis — a benefit that GLP-1 monotherapy alone cannot fully replicate. The key engineering challenge is balancing these opposing glycaemic effects, which explains why all approved and late-stage candidates in this class feature carefully calibrated receptor selectivity ratios.

Three candidates illustrate the breadth of this class. Mazdutide (IBI362), developed by Innovent Biologics, became the first dual GLP-1/glucagon agonist to receive regulatory approval — in China in June 2025. Its C16 fatty acid modification enables once-daily dosing, and Phase 3 data show 14.6% weight loss at 48 weeks alongside meaningful improvements in liver fat content. Survodutide (BI 456906), Boehringer Ingelheim’s candidate currently in Phase 3, achieved 15.7% weight loss at 46 weeks in Phase 2 trials, with a greater than 50% relative reduction in liver fat — a signal of particular interest for the large population of obesity patients with concurrent MASH. Cotadutide (MEDI0382, AstraZeneca) is also showing promise specifically in MASH treatment with improved liver histology.

“Triple agonism produces superior metabolic effects compared to dual agonists, with enhanced weight loss, improved glucose tolerance, and reduced hepatic steatosis — without causing hyperglycemia.”

Triple agonists: retatrutide and the race to match bariatric surgery

Triple GLP-1/GIP/glucagon agonists represent the most ambitious pharmacological strategy in the obesity pipeline, integrating all three receptor mechanisms into a single molecule to produce metabolic effects that may approach bariatric surgery efficacy. Retatrutide (LY3437943), developed by Eli Lilly, is the most advanced candidate and has produced the most striking clinical data seen yet in obesity pharmacotherapy.

In Phase 2 trials, retatrutide at the 12 mg dose produced 24.2% weight loss at 48 weeks. Critically, 83% of patients at the highest dose achieved at least 15% weight loss — a responder rate that begins to approach what bariatric surgery delivers. Beyond weight, the drug produced significant improvements in HbA1c, lipid profiles, and liver enzymes. The drug’s balanced tri-agonist activity provides three complementary mechanisms: GLP-1 for insulin secretion, appetite suppression, and gastric emptying delay; GIP for enhanced insulinotropic effects, central satiety, and adipose tissue remodeling; and glucagon for energy expenditure, hepatic lipolysis, and amino acid metabolism.

Multiple other pharmaceutical companies are also developing triple agonist candidates with varying receptor selectivity profiles. SAR441255 (Sanofi) is in Phase 1/2 trials; HM15211 (Hanmi Pharmaceutical) is a long-acting candidate designed for weekly dosing; and Sun Pharma has filed patents on novel peptide sequences targeting all three receptors. The competitive intensity in this space, tracked by PatSnap’s patent intelligence platform, reflects the industry’s conviction that triple agonism will define the next generation of obesity pharmacotherapy.

The superior efficacy of multi-agonists cannot be fully explained by simple additive effects. Emerging evidence points to complex receptor interactions: GLP-1R and GIPR can form heterodimers or influence each other’s signaling when co-expressed in the same tissue; multi-agonists may exhibit different G-protein versus β-arrestin signaling profiles compared to native hormones; and different receptor expression patterns across tissues allow for targeted metabolic effects in adipose, hepatic, and muscle tissue simultaneously.

GLP-1/amylin combinations and mechanistically distinct alternatives

CagriSema — the combination of semaglutide and cagrilintide (a long-acting amylin analog developed by Novo Nordisk) — demonstrates that combining GLP-1 agonism with a non-incretin mechanism can nearly double efficacy over the same treatment period: 15.6% weight loss at 32 weeks versus 8.1% with semaglutide alone in Phase 2 trials. This result validates the principle that mechanistically orthogonal combinations can outperform any single pathway.

Amylin is a pancreatic hormone co-secreted with insulin. It regulates glucose homeostasis through three distinct actions: slowing gastric emptying to reduce nutrient absorption rate; acting on the area postrema and nucleus tractus solitarius in the brainstem to suppress appetite centrally; and suppressing postprandial glucagon secretion to reduce hepatic glucose output. Critically, amylin’s mechanisms do not overlap with GLP-1R pathways — they are genuinely complementary, which explains the synergistic weight loss observed with CagriSema. Novo Nordisk has advanced the combination into a Phase 3 program enrolling patients with obesity and type 2 diabetes.

NK2R agonists: a mechanistically distinct alternative

NK2R (neurokinin-2 receptor) agonists represent a completely different pharmacological approach from incretin-based therapies. Genetic and preclinical studies have identified NK2R as a promising target for obesity and type 2 diabetes. The mechanism involves three pathways: peripheral NK2R activation increases metabolic rate and energy expenditure; central NK2R signaling reduces food intake without the nausea associated with GLP-1R agonism; and NK2R activation improves glucose utilization through insulin sensitization independent of weight loss. This nausea-free appetite suppression profile may make NK2R agonists particularly valuable for patients who cannot tolerate the gastrointestinal side effects that affect 20–40% of patients on incretin-based therapies, as reported in clinical literature reviewed by NIH-funded investigators.

Bimagrumab: preserving muscle during weight loss

Bimagrumab is a monoclonal antibody targeting activin type II receptors, blocking myostatin and related proteins that inhibit muscle growth. Its clinical profile is unique: it preserves or increases lean muscle mass during weight loss — directly addressing one of the most significant concerns with aggressive pharmacological weight reduction, namely sarcopenia. For patients with sarcopenic obesity (excess fat combined with low muscle mass), bimagrumab may offer a profile that no incretin-based therapy can match. The loss of lean mass during rapid weight loss is a recognised concern documented in obesity research published by NEJM and other peer-reviewed journals.

Oral small-molecule GLP-1R agonists

Orforglipron (Eli Lilly) and danuglipron (Pfizer) represent a new class of non-peptide, orally bioavailable GLP-1R agonists. Phase 2 data show 8–15% weight loss at 36 weeks — somewhat below injectable peptides, but the oral route offers meaningful advantages in convenience and adherence. Both molecules are currently in Phase 3 trials. For the large population of patients who decline injectable therapies, oral small-molecule GLP-1R agonists may substantially expand treatment access.

GIPR antagonists combined with GLP-1R agonists

An alternative strategy to GIPR agonism is GIPR antagonism combined with GLP-1R activation, exemplified by maridebart cafraglutide (Amgen). The rationale is that blocking GIPR may reduce adipocyte lipid storage, prevent GIPR desensitization, and enhance GLP-1R signaling through receptor crosstalk — a fundamentally different hypothesis from the tirzepatide approach. Clinical trials are ongoing to determine whether GIPR antagonism offers advantages over GIPR agonism, and the outcome will have significant implications for understanding the true role of GIP signaling in human obesity.

FGF21 analogs

Fibroblast growth factor 21 (FGF21) is a metabolic hormone that enhances insulin sensitivity, increases energy expenditure, improves lipid metabolism, and reduces hepatic fat. Clinical development has been challenging due to the need for frequent dosing and modest efficacy with first-generation compounds, but next-generation analogs with improved pharmacokinetics are in active development and may prove particularly useful in combination regimens targeting MASH.

Clinical pipeline, efficacy hierarchy, and the road ahead

The pharmaceutical industry has invested heavily in next-generation obesity medications, with over 30 dual and triple agonist programs currently in clinical development. The pipeline spans multiple phases: tirzepatide is already approved; CagriSema, survodutide, and retatrutide are in Phase 3; and multiple triple agonist candidates from Sanofi, Hanmi, and others are in Phase 2, alongside oral GLP-1R agonists and NK2R agonists. According to data tracked by PatSnap’s life sciences intelligence platform, patent filing activity in multi-agonist obesity drugs has accelerated significantly over the past three years.

Based on available clinical trial data, the efficacy ranking for weight loss currently stands as follows: triple agonists (retatrutide, 24.2% at 48 weeks) lead; followed by dual GLP-1/GIP (tirzepatide, 22.5% at 72 weeks); then dual GLP-1/glucagon (survodutide, 15.7% at 46 weeks); GLP-1/amylin (CagriSema, 15.6% at 32 weeks); and GLP-1 monotherapy (semaglutide 2.4 mg, 14.9% at 68 weeks). It is important to note that these trials differ in duration and patient populations, making direct comparisons approximate rather than definitive, as noted in clinical trial registries maintained by ClinicalTrials.gov.

Gastrointestinal side effects — nausea, vomiting, and diarrhea — remain the primary limitation across all incretin-based therapies, affecting 20–40% of patients. Multi-agonist approaches have not significantly reduced these effects compared to GLP-1 monotherapy. Dual and triple agonists do, however, demonstrate favorable cardiovascular profiles, with reductions in blood pressure, inflammation, and atherogenic lipids. Cost and access remain structural barriers: novel biologics cost approximately $1,000–$1,500 per month, limiting widespread adoption. Long-term durability is also a concern, with weight regain after discontinuation observed across drug classes.

Future treatment strategies will likely involve personalised selection of multi-agonist therapies based on patient phenotype, genetic factors, and comorbidity profiles. Patients with MASH may be best served by glucagon-containing combinations; those with sarcopenic obesity may benefit from bimagrumab combinations; patients intolerant of injectables may use oral small-molecule GLP-1R agonists; and those with genetic polymorphisms in incretin receptor genes may show differential responses to GIP-based versus amylin-based approaches. Combination strategies are also being explored — including GLP-1R agonists paired with SGLT2 inhibitors for complementary cardiorenal protection, and multi-agonists combined with bariatric surgery to optimise pre- and post-surgical outcomes.

The expanding armamentarium of multi-mechanism drugs targeting obesity and metabolic disease represents one of the most significant advances in endocrinology and metabolism in decades. As these agents progress through clinical development and gain regulatory approval, the field is moving toward a model where the choice of obesity pharmacotherapy is as individualised as the choice of cancer treatment — matched to the specific biological drivers of each patient’s condition.