Peptides for Metabolism: Metabolic Peptides and What They Do

Key Takeaways

• What this covers: Three major categories of metabolic peptides: GLP-1 class drugs (FDA-approved), MOTS-c (experimental; endogenous mitochondrial peptide under investigation), and AOD-9604 (failed Phase 2b obesity trial; removed from Category 2; not eligible for 503A compounding).
• Regulatory status: As of April 2026, GLP-1 receptor agonists including semaglutide and tirzepatide are FDA-approved for metabolic indications. MOTS-c in injectable form is not FDA-approved for any indication. AOD-9604 has been removed from the FDA Category 2 list; with no Category 1 placement, no USP/NF monograph, and no approved drug product precedent, it is not eligible for 503A compounding.
• Evidence stage: GLP-1 class drugs have extensive Phase 3 RCT data. MOTS-c has foundational animal and mechanistic data with no completed human trials. AOD-9604 has a failed Phase 2b human obesity trial.
• Body composition caveat: GLP-1 therapy produces weight loss with a substantial fat-free mass component. Muscle preservation alongside GLP-1-driven weight loss is an active and unresolved clinical question.

What Are Metabolic Peptides?

A metabolic peptide, broadly defined, is any amino acid sequence with documented or proposed effects on energy homeostasis, glucose regulation, fat metabolism, or body composition. The category spans a vast regulatory and evidentiary spectrum: from GLP-1 receptor agonists with tens of thousands of patient-years of clinical trial safety data to MOTS-c, which as of April 2026 has no completed human efficacy trial in any form. Treating these compounds as a unified category implies a comparability that does not exist.

Understanding metabolic peptides requires compound-by-compound evaluation of: the target receptor or pathway, the evidence type and quality, the regulatory status, and the access pathway. This article covers the three most searched and discussed categories: GLP-1 class drugs, MOTS-c, and AOD-9604.

Petsas and colleagues, in a 2025 review in Molecules, described protein-ligand interactions in cardiometabolic drug targets [biochemistry review] — relevant context for why peptide drug development has produced compounds of dramatically different regulatory outcomes.

What Is MOTS-c?

MOTS-c (mitochondrial open reading frame of the 12S rRNA-c) is a 16-amino-acid peptide encoded not by the nuclear genome but by mitochondrial DNA — a mitochondrial-derived peptide (MDP). This is a distinctive characteristic: the vast majority of known endogenous peptide hormones are nuclear-genome-encoded. MOTS-c's mitochondrial origin means it functions as a direct signal connecting cellular energy status (mitochondrial function) to systemic metabolic regulation.

MOTS-c was first identified by Lee and colleagues at the University of Southern California, published in a landmark 2015 paper in Cell Metabolism, identified MOTS-c as a mitochondrial-derived peptide that promotes metabolic homeostasis and reduces obesity and insulin resistance in mice [animal model]. Endogenous MOTS-c is found in human plasma, skeletal muscle, and liver, with circulating levels that appear to decline with age and metabolic disease — a pattern that has attracted research interest in its potential role in age-related metabolic decline.

How MOTS-c Works in the Body

MOTS-c operates through at least two distinct mechanisms: AMPK-dependent metabolic signaling in peripheral tissues, and — notably — direct nuclear translocation during metabolic stress.

AMPK activation and glucose homeostasis

The primary pathway identified in early MOTS-c research involves activation of AMPK (AMP-activated protein kinase), the cellular energy sensor that triggers glucose uptake, fat oxidation, and mitochondrial biogenesis when cellular energy status is low. Lee and colleagues, in their 2015 Cell Metabolism paper, demonstrated that MOTS-c activates AMPK in skeletal muscle, stimulating glucose uptake and reducing insulin resistance in mice [animal model]. A second study by Lee and colleagues in Free Radical Biology and Medicine in 2016 further established MOTS-c's role in muscle and fat metabolism through the same AMPK-dependent pathway. Yin and colleagues, in a 2021 study in Pharmacological Research, extended this work using animal and cell models of gestational diabetes, showing that MOTS-c MOTS-c in a gestational diabetes animal model models, providing clinical-adjacent evidence of glucose-regulating effects [animal / cell model of human condition].

Nuclear translocation: a unique mechanism

In a finding that distinguished MOTS-c from other peptide hormones, Kim and colleagues published a 2018 study in Cell Metabolism demonstrating that MOTS-c translocates from the cytoplasm to the cell nucleus in response to metabolic stress, where it directly regulates nuclear gene expression [in vitro / animal model]. This nuclear localization allows MOTS-c to act as a transcription co-regulator — not merely a circulating signal that activates surface receptors, but a molecule that enters the genome's operational machinery. Zheng and colleagues, in a 2023 review in Frontiers in Endocrinology, characterized this discovery as distinguishing MOTS-c from other peptide hormones and as a basis for further mechanistic research.

Liver metabolism and NASH

Lu and colleagues, in a 2024 study in Cell Reports, showed that in animal NASH models MOTS-c interacted with Bcl-2 signaling [animal model], providing evidence of liver-specific metabolic changes beyond muscle and adipose tissue. Kong and colleagues, in a 2023 review in the Diabetes and Metabolism Journal, reviewed MOTS-c in diabetes and aging-related diseases, connecting its mechanisms to metabolic conditions including type 2 diabetes and age-related metabolic decline. Wan and colleagues, in a 2023 review in the Journal of Translational Medicine, synthesized the evidence on MOTS-c in metabolism and aging.

What Is AOD-9604?

AOD-9604 (also designated AOD9604 or fragment 177-191) is a synthetic peptide corresponding to amino acids 177-191 at the C-terminus of full-length human growth hormone, with an added N-terminal tyrosine residue for metabolic stability. It was developed to test whether hGH's fat-metabolizing activity could be separated from its insulin-antagonizing effects by isolating the C-terminal domain.

Heffernan and colleagues, in a 2001 study in Endocrinology, demonstrated in obese and beta-3-adrenergic receptor knockout mice that AOD-9604 showed lipolytic and antilipogenic activity without the insulin-antagonizing effects of full-length hGH [animal model]. Halford, in a 2006 review in Current Opinion in Investigational Drugs, placed AOD-9604 in late-2000s obesity pipeline, a pipeline that would prove to produce mostly failed candidates. The pivotal Phase 2b obesity trial of AOD-9604 in humans did not meet its primary weight-loss endpoint versus placebo, and the compound was not subsequently advanced to FDA approval [human Phase 2b trial outcome as reported in sponsor disclosures; no peer-reviewed publication of the Phase 2b failure identified as of April 2026]. AOD-9604 received a self-affirmed Generally Recognized as Safe (GRAS) notification for specific dietary supplement uses — a narrow safety determination for food ingredient use that does not constitute FDA approval as a drug, does not authorize therapeutic claims, and does not apply to injectable or compounded forms. As of April 2026, AOD-9604 has been removed from the FDA Category 2 bulk drug substances evaluation list; it is not on the Category 1 list, has no USP/NF monograph, and does not have an approved drug product precedent, so it is not eligible for 503A compounding.

GLP-1 Class Peptides: FDA-Approved and Best-Studied

GLP-1 (glucagon-like peptide-1) is a 30-amino-acid incretin hormone produced by intestinal L-cells in response to food intake. It stimulates glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite through central hypothalamic signaling. GLP-1 receptor agonists are synthetic analogs engineered to resist the rapid enzymatic degradation that limits endogenous GLP-1's half-life to approximately 2 minutes, extending pharmacological activity to hours or weeks depending on the formulation.

Liu and colleagues, in a comprehensive 2025 review in Drug Design, Development and Therapy, covered the clinical applications of incretin-based therapies for metabolic disease across approved indications. Davies and colleagues, in a 2026 study in Diabetes, Obesity and Metabolism, examined how the GIP component of tirzepatide (a dual GLP-1/GIP agonist) contributes to metabolic outcomes, comparing GIPR agonism versus GIPR antagonism in male mice, noting that GIP's contribution to tirzepatide's superior efficacy over GLP-1 alone is an area of active mechanistic investigation [animal model]. Wong and colleagues, in a 2026 study in Obesity, examined reduced-frequency GLP-1 dosing outcomes, contributing to the understanding of dosing strategy in long-term metabolic management [case series].

The Body Composition Question

GLP-1 therapy produces substantial and consistent weight loss, but the composition of that weight loss — how much is fat and how much is lean mass including muscle — is a clinically significant open question. As weight loss from GLP-1 therapy has become common practice, preservation of lean mass has emerged as a primary concern, particularly given that skeletal muscle mass has independent metabolic significance beyond body weight.

Eisa and colleagues, in a 2026 systematic review in Diabetes, Obesity and Metabolism, examined lean mass changes with incretin therapy versus lifestyle intervention across available trials, finding that GLP-1 therapy produced lean mass reductions compared to lifestyle intervention, raising the clinical question of whether muscle preservation strategies should accompany GLP-1 use [systematic review of human RCTs]. Batsis and colleagues, in a 2026 systematic review in the Annals of Internal Medicine, provided meta-level evidence on body composition changes with incretin-based weight loss, confirming that fat-free mass loss is a consistent feature of GLP-1-driven weight reduction [systematic review]. Koceva and colleagues, in a 2025 review in Medicina, reviewed incretin therapy and skeletal muscle, finding mixed evidence on muscle quality outcomes. Ryan, in a 2025 review in Reviews in Endocrine and Metabolic Disorders, explicitly framed the question: muscle preservation during obesity pharmacotherapy? [review].

Stefanakis and colleagues, in a 2024 comprehensive review in Metabolism, examined whole-body effects of weight loss modalities across multiple weight loss approaches, providing a whole-body systems perspective on what GLP-1-driven weight loss does beyond fat tissue [review]. Tyurina and colleagues, in a 2026 study in Kardiologiia, reported semaglutide's effects on metabolic markers simultaneously in obese patients [human observational study; design should be confirmed against the primary publication].

What the Research Shows: Evidence by Level

The evidence landscape for metabolic peptides is defined by the compound category. As of April 2026, the categories have dramatically different evidence tiers.

• GLP-1 class peptides (semaglutide, tirzepatide)
  • Volume of evidence: Extensive; multiple Phase 3 RCTs including SELECT (semaglutide, N=17,604), SURMOUNT-1 (tirzepatide, N=2,539), and STEP trials
  • Key finding: In their respective Phase 3 trials, semaglutide 2.4mg (STEP 1) and tirzepatide (SURMOUNT-1) produced average body weight reductions of approximately 15% (semaglutide 2.4mg) and up to ~20% (tirzepatide 15mg) versus placebo over 68–72 weeks. In the SELECT trial, semaglutide 2.4mg was associated with a reduction in a composite cardiovascular outcome in adults with pre-existing cardiovascular disease and overweight/obesity — a benefit specific to that labeled indication and patient population. Individual results vary. Improvements in triglycerides, blood pressure, and HbA1c are also reported.
  • Strength of inference: Highest — established by multiple large RCTs
• MOTS-c (injectable, experimental)
  • Volume of evidence: Foundational in vitro and animal studies; no completed human efficacy trials as of April 2026
  • Key finding: AMPK activation and glucose metabolism improvement in rodent and cell models; nuclear translocation during metabolic stress; liver NASH protection in animal models
  • Strength of inference: Establishes biological plausibility and mechanism; does not establish human efficacy or safety
• AOD-9604 (removed from FDA Category 2; not eligible for 503A compounding)
  • Volume of evidence: Substantial preclinical data; one Phase 2b human trial (failed primary endpoint)
  • Key finding: Did not meet its primary weight-loss endpoint versus placebo in the pivotal Phase 2b obesity trial, despite promising preclinical fat-metabolism data
  • Strength of inference: Preclinical findings not replicated in adequately powered human trial; not legally compoundable under Section 503A as of April 2026

How to Access Metabolic Peptides

Access pathways vary significantly and must be assessed compound by compound.

GLP-1 receptor agonists (semaglutide, tirzepatide) are FDA-approved prescription medications requiring a prescription from a licensed US healthcare provider. They are dispensed through licensed pharmacies and require ongoing clinical supervision. As of April 2026, Superpower connects members with licensed healthcare providers who evaluate whether FDA-approved GLP-1 medications or, where clinically indicated and where a 503A clinical-difference pathway applies, compounded GLP-1 preparations are appropriate. Superpower does not prescribe or dispense medications; eligibility, product selection, and prescribing are determined by the treating provider. Compounded tirzepatide may be dispensed by licensed 503A pharmacies only on a patient-specific prescription basis and only where the prescribing provider has documented a clinical difference from the FDA-approved product — for example, a formulation, strength, or ingredient change that addresses a specific patient need. The "essentially a copy" prohibition under 21 U.S.C. § 353a(b)(2) otherwise precludes 503A compounding of tirzepatide now that the shortage is resolved. Compounded preparations are not FDA-approved products; their regulatory status differs materially from FDA-approved tirzepatide. See individual compound pages for the specific regulatory status of the product you receive.

Compounded GLP-1 products were previously available through 503A and 503B compounding pharmacies under FDA's shortage-resolution authority while semaglutide and tirzepatide were on the FDA drug shortage list. The FDA declared those shortages resolved in 2025, which ended the shortage-based compounding pathway. As of April 2026, legally compounded semaglutide or tirzepatide is generally limited to narrow patient-specific clinical-difference scenarios under Section 503A.

MOTS-c in injectable form: as of April 2026, there is no legal pathway to obtain injectable MOTS-c for human therapeutic use in the United States. Products labeled as MOTS-c sold through online research chemical vendors are not regulated by the FDA. "Research Use Only" labeling does not make these products legal for human therapeutic use — FDA applies the intended-use doctrine based on actual commercial context, not label disclaimers alone. Superpower does not prescribe, sell, or facilitate access to MOTS-c in any form.

AOD-9604: as of April 2026, AOD-9604 has been removed from the FDA Category 2 bulk drug substances evaluation list. With no Category 1 placement, no USP/NF monograph, and no approved drug product precedent, AOD-9604 is not eligible for 503A compounding. Products sold as AOD-9604 through online vendors operate outside FDA oversight. Superpower does not currently offer or facilitate access to AOD-9604.

Safety Considerations

Safety profiles differ substantially across the three categories.

Known adverse effects

For GLP-1 receptor agonists, the adverse event profile is well-characterized from large trials: nausea, vomiting, and diarrhea occur in 10-40% of patients; constipation is also reported; pancreatitis (rare), gallbladder disease, and injection site reactions are documented [human RCT]. The body composition consequence — lean mass loss alongside fat loss — is a metabolic safety consideration, not an acute adverse event [human RCT / systematic review]. For MOTS-c, no human clinical safety data exists. For AOD-9604, the Phase 2b trial did not report significant adverse effects beyond placebo, and the self-affirmed GRAS notification addresses narrow dietary supplement food ingredient safety, not therapeutic or injectable safety; long-term safety data at any dose does not exist.

Populations who should exercise caution

• Individuals with personal or family history of MEN2 or medullary thyroid carcinoma: GLP-1 receptor agonists carry FDA labeling regarding risk based on rodent model findings; these individuals should not use GLP-1 drugs.
• Individuals with history of pancreatitis: GLP-1 receptor agonists are associated with pancreatitis risk; prior pancreatitis requires clinical evaluation before use.
• Competitive athletes: AOD-9604 is prohibited under the WADA Prohibited List (category S2, peptide hormones, growth factors, related substances and mimetics). MOTS-c is not explicitly named on the 2026 WADA Prohibited List; WADA's Section S0 prohibits non-approved substances with no governmental regulatory health authority approval for human therapeutic use, which WADA may interpret to include experimental peptides. Athletes subject to WADA testing should treat both compounds as prohibited and consult their sport's anti-doping authority before use.
• Individuals with active cancer: MOTS-c modulates cellular stress and oncogenic pathways in preclinical cancer models in mixed directions — Yin and colleagues, in a 2024 study in Advanced Science, reported preclinical MOTS-c effects in an ovarian cancer model, while effects in other tumor types and in humans are uncharacterized. Given the absence of human safety data in active-cancer populations, individuals with active cancer should not use MOTS-c without oncologist input.
• Pregnant or breastfeeding individuals: GLP-1 drugs should not be used during pregnancy; MOTS-c and AOD-9604 have no reproductive safety data.

What is not yet known

For MOTS-c, essentially the entire human safety and efficacy profile is unknown. Long-term metabolic effects, optimal dosing, delivery route, and drug interactions are all uncharacterized. For GLP-1 drugs, the long-term consequences of lean mass reduction over extended treatment are under active investigation. The clinical implications of Lu and colleagues' 2023 finding — in a myocardial ischemia-reperfusion animal model, MOTS-c reduced ferroptosis and lung injury markers — indicating broad cytoprotective actions beyond metabolic tissue are not characterized in humans.

Which Biomarkers Are Relevant for Metabolic Peptide Evaluation?

Metabolic peptides act on systems that are directly measurable through standard laboratory testing. Baseline characterization before initiating any metabolic intervention — pharmaceutical or otherwise — is the foundation for interpreting downstream changes.

• Fasting glucose and insulin: Primary markers of glucose homeostasis and insulin sensitivity. Fasting glucose and fasting insulin together allow calculation of HOMA-IR (insulin resistance index), the most commonly used metabolic assessment of insulin sensitivity outside a formal glucose clamp.
• HbA1c: A 90-day integrated measure of blood glucose. HbA1c is the primary efficacy endpoint in GLP-1 drug diabetes trials and provides the cleanest single-number metabolic baseline.
• Triglycerides: Triglycerides directly reflect fat metabolism and liver lipid handling — the primary target systems of both GLP-1 drugs and AOD-9604's proposed mechanism. Changes in triglycerides are among the earliest metabolic signals visible after GLP-1 initiation.
• IGF-1: For compounds that interact with the GH axis (AOD-9604, growth hormone secretagogues), IGF-1 provides baseline context for GH-axis activity. AOD-9604 was designed to avoid stimulating IGF-1 elevation, but baseline IGF-1 characterizes the GH axis before any intervention.
• hs-CRP: Adipose tissue is an active inflammatory organ. High-sensitivity C-reactive protein reflects systemic low-grade inflammation associated with metabolic dysfunction and is measurably reduced by GLP-1 therapy in some trial populations.
• HDL cholesterol: HDL cholesterol is consistently improved by GLP-1-driven weight loss and provides a cardiovascular metabolic marker complementary to triglycerides.
• Body composition (DEXA or equivalent): Standard blood panels do not directly measure fat vs. lean mass. Where available, body composition measurement provides the most direct assessment of metabolic peptide effects on tissue composition — including the muscle preservation question central to GLP-1 therapy monitoring.

Establishing these baselines before initiating any metabolic intervention makes subsequent measurements interpretable. That is the core of Superpower's approach to preventive metabolic health: understand the biology first, then track the changes.

IMPORTANT SAFETY INFORMATION

This article covers compounds with substantially different regulatory statuses. GLP-1 receptor agonists (semaglutide, tirzepatide) are FDA-approved prescription medications for type 2 diabetes and chronic weight management; Superpower connects members with licensed healthcare providers who evaluate whether FDA-approved GLP-1 medications or, where clinically indicated and where a 503A clinical-difference pathway applies, compounded GLP-1 preparations are appropriate. Superpower does not prescribe or dispense medications; eligibility, product selection, and prescribing are determined by the treating provider. MOTS-c in injectable form is not approved by the FDA for any medical use; no completed human clinical trials exist for its safety or efficacy; Superpower does not prescribe, sell, or facilitate access to injectable MOTS-c. AOD-9604 has been removed from the FDA Category 2 bulk drug substances evaluation list as of April 2026; with no Category 1 placement, no USP/NF monograph, and no approved drug product precedent, AOD-9604 is not eligible for 503A compounding. Superpower does not currently offer or facilitate access to AOD-9604.

GLP-1 receptor agonists: do not use if you have a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. Risk of pancreatitis has been reported; prior pancreatitis requires clinical evaluation before use. Common adverse effects: nausea, vomiting, diarrhea, constipation, injection site reactions. Gallbladder disease including cholelithiasis has been reported. Lean mass loss alongside fat loss is a documented metabolic consequence requiring monitoring.

Warnings for experimental compounds: MOTS-c has no human clinical safety data. Products sold as MOTS-c or AOD-9604 through online vendors are not subject to FDA manufacturing oversight. Competitive athletes should be aware that AOD-9604 is on the WADA Prohibited List.

As of April 2026, no completed human efficacy trials for injectable MOTS-c have been published. Preclinical metabolic findings for MOTS-c and AOD-9604 cannot be extrapolated to confirm efficacy in humans. Full prescribing information for FDA-approved GLP-1 medications is available in their respective FDA-approved labeling.

Disclaimer: IMPORTANT: This article discusses compounds with different regulatory statuses. GLP-1 receptor agonists (semaglutide, tirzepatide) are FDA-approved prescription medications; compounded GLP-1 preparations dispensed by 503A pharmacies on a patient-specific basis are distinct products from FDA-approved GLP-1 medications and are not FDA-approved themselves. MOTS-c and AOD-9604 are not FDA-approved for human use; AOD-9604 has been removed from the FDA Category 2 bulk drug substances list and is not eligible for 503A compounding. Superpower connects members with licensed healthcare providers who determine whether FDA-approved GLP-1 medications or, where appropriate, compounded GLP-1 preparations are clinically indicated. This content is for educational purposes only.