AOD9604 is a modified growth-hormone fragment whose oral obesity program failed to establish useful weight loss. Semaglutide activates the GLP-1 receptor and produced substantially greater weight reduction than placebo in STEP 1. No direct randomized comparison establishes their relative effect or safety; the informative contrast is between their different controlled human results.
Research reviewed October 15, 2026. Educational information only.
A fat-related hypothesis and an appetite-regulating receptor
AOD9604 is Tyr-hGH 177–191, a 16-residue peptide based on the carboxyl end of growth hormone with an added amino-terminal tyrosine. It was developed to preserve fat-related effects observed with growth-hormone fragments while avoiding the growth and glucose effects of the full hormone. Animal studies supplied the initial rationale, and the human safety program monitored the growth-related hormone IGF-1 and glucose handling. AOD9604 is a different molecule from full-length growth hormone.
Semaglutide is a modified analogue of glucagon-like peptide 1, or GLP-1. It activates the GLP-1 receptor and reduces calorie intake through appetite regulation, while also affecting glucose control. The tested injection, approved tablets and other semaglutide products have formulation-specific evidence. The comparison here centers on the injection used in STEP 1 and the oral AOD9604 obesity program; it does not assume all formulations produce identical effects.
The main differences
What is each molecule designed to do?
Their biological rationales differ, and a plausible mechanism needs a controlled clinical outcome before it supports an obesity-treatment claim.
AOD-9604
AOD9604 is a 16-residue modified growth-hormone fragment, Tyr-hGH 177–191. Its development sought fat-related activity without the full hormone’s insulin-like growth factor 1 (IGF-1) and glucose effects; the human report monitored those outcomes.
Semaglutide
Semaglutide is a modified glucagon-like peptide 1 (GLP-1) analogue that activates the GLP-1 receptor. Appetite and calorie-intake regulation help explain its weight effects; its approved products have formulation-specific evidence.
What happened in the principal placebo-controlled obesity trial?
The AOD trial used an oral product for 24 weeks; STEP 1 used semaglutide injections for 68 weeks. Both included diet/activity support. Their separate trials cannot estimate a direct treatment difference.
AOD-9604
In OPTIONS, 502 adults with obesity were randomized to oral AOD9604 or placebo alongside diet and exercise. FDA’s review describes failure to establish greater weight loss, with the primary weight assessment at 12 weeks during 24 weeks of treatment. Complete numerical group results were not available in the accessed report.
Semaglutide
In STEP 1, 1,961 adults without diabetes received semaglutide or placebo plus lifestyle support. At 68 weeks, mean weight fell 14.9% versus 2.4%; the adjusted additional loss was 12.4 percentage points (95% CI 11.5–13.4). The analysis includes treatment stopping and the start of other weight treatments.
Can animal fat-metabolism findings settle the human comparison?
Animal metabolic measurements and human long-term weight change answer different questions. Each preparation also needs its own route and formulation context.
AOD-9604
Genetically obese rats gained less weight and had greater fat-breakdown activity with AOD9604. Those findings supplied a rationale for clinical development, but the larger oral human program did not establish useful obesity efficacy.
Sources
- Ng FM, Sun J, Sharma L, Libinaka R, Jiang WJ, Gianello R. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone research. 2000;53(6):274–278. doi:10.1159/000053183. PMID:11146367.
- U.S. Food and Drug Administration. December 4, 2024 Pharmacy Compounding Advisory Committee Meeting. Official transcript, topic 2: AOD9604-related bulk drug substances.
Semaglutide
In STEP 1, 1,961 adults without diabetes received semaglutide or placebo plus lifestyle support. At 68 weeks, average weight fell 14.9% with semaglutide and 2.4% with placebo. This measured human weight change does not depend on converting an animal fat-breakdown finding into predicted weight loss.
What can the exposure evidence tell us?
An elimination half-life describes decline in a measured drug, not a guaranteed duration or size of clinical benefit. Route-specific results remain essential.
AOD-9604
The human safety program used intravenous AOD9604, oral capsules and oral tablets in distinct studies. It does not supply one verified elimination estimate for every preparation. The oral obesity result cannot establish the effects of an injected product.
Semaglutide
The current Wegovy label gives an approximately one-week semaglutide elimination half-life. That product pharmacology does not predict an individual weight response or establish how much weight remains off after discontinuation.
Do the data identify AOD9604 as a safer option?
There is no direct randomized safety comparison. Known product warnings and missing evidence need different interpretations.
AOD-9604
The pooled report found no overall IGF-1 rise or worsened glucose tolerance, but includes possibly related severe chest tightness and serious diarrhea in distinct early studies. FDA flags immune-reaction and impurity concerns and insufficient safety information for compounded AOD9604.
Sources
- Stier H, Vos E, Kenley D. Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans. Journal of Endocrinology and Metabolism. 2013;3(1–2):7–15. DOI: 10.4021/jem157w.
- U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Agency assessment; accessed October 15, 2026.
Semaglutide
In STEP 1, 4.5% of semaglutide recipients stopped treatment because of digestive events, versus 0.8% with placebo. The approved label describes gastrointestinal, pancreatic, gallbladder, kidney and other warnings, including a rodent thyroid-tumor boxed warning with uncertain human relevance. These data cannot rank its safety against AOD9604.
Sources
- Wilding JPH, Batterham RL, Calanna S, Davies M, Van Gaal LF, Lingvay I, McGowan BM, Rosenstock J, Tran MTD, Wadden TA, Wharton S, Yokote K, Zeuthen N, Kushner RF, STEP 1 Study Group. Once-Weekly Semaglutide in Adults with Overweight or Obesity. The New England journal of medicine. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183. PMID:33567185.
- Novo Nordisk. WEGOVY (semaglutide) injection and tablets: U.S. prescribing information. Revised June 2026. DailyMed; accessed October 15, 2026.
What the oral AOD9604 program established
The largest AOD9604 obesity study, called OPTIONS or METAOD006, randomized 502 adults with obesity to oral AOD9604 or placebo after a run-in period. Treatment lasted 24 weeks, and both groups received a diet and exercise program. FDA’s review identifies weight loss after 12 weeks among the primary efficacy outcomes. The study did not establish a meaningful treatment advantage over placebo; the sponsor ended obesity development after the failed result.
This conclusion is more specific than saying that the molecule cannot have any biological action. A smaller 12-week trial had reported modest between-group weight differences with a non-linear dose response. FDA found the published detail too limited to assess that finding securely, and the larger trial did not establish the anticipated efficacy. The available official summary does not provide complete group means and confidence intervals for OPTIONS, so a numerical human AOD-versus-semaglutide effect cannot be calculated.
Participant counts also need care. The 2013 safety paper reports 534 enrolled and 502 randomized in METAOD006; its 893-person total pools the safety populations of six different studies. These are different denominators and do not mean that 893 people received active AOD9604 in one obesity trial.
What STEP 1 measured with semaglutide
STEP 1 randomized 1,961 adults without diabetes who had obesity, or overweight with at least one weight-related condition, to weekly semaglutide 2.4 mg or placebo injections for 68 weeks. Both groups received lifestyle counseling. Average body weight fell 14.9% with semaglutide and 2.4% with placebo. The adjusted difference was 12.4 percentage points in favor of semaglutide (95% confidence interval 11.5–13.4 points).
These estimates include outcomes after assigned treatment stopped or another weight intervention began, an approach called the treatment-policy estimand. It describes the effect of assignment under the trial conditions and depends on the statistical handling of missing measurements. It is different from an estimate assuming everyone continued the trial medicine. STEP 1 therefore provides a clearly defined controlled human result, while the AOD program provides a failed efficacy test with incompletely published numerical detail.
The two trials differ in duration, product, route, eligibility and analysis. Their separate placebo groups show what happened within each experiment; they do not turn the studies into a direct AOD9604-versus-semaglutide trial.
Why route and formulation matter for exposure
The current Wegovy label reports an elimination half-life of approximately one week for semaglutide. This means the measured circulating drug declines relatively slowly during its elimination phase. It helps explain the product’s pharmacology but does not predict the amount of weight one person will lose or how long weight loss will persist after stopping.
AOD9604’s human program included short intravenous studies as well as oral capsules and tablets. The pooled safety report does not establish one transferable human elimination estimate covering those preparations. In particular, the failed oral obesity program cannot verify the exposure, effectiveness or safety of an injected product sold under the same peptide name. A shared claim of fat loss cannot overcome the missing route-specific evidence.
The safety results do not establish a safer alternative
The six-study AOD9604 report did not find higher IGF-1 or worsened glucose tolerance overall, and selected antibody testing found no anti-peptide antibodies. Its detailed results nevertheless include a severe chest-tightness event during an intravenous study and a serious diarrhea event in an oral study, both considered possibly related to treatment. The abstract’s broad reassurance is therefore incomplete without the study-specific events. FDA also flags immune-reaction, impurity and characterization concerns for compounded AOD9604 and considers the human safety information insufficient.
In STEP 1, nausea and diarrhea were common; digestive adverse events caused treatment stopping in 4.5% with semaglutide and 0.8% with placebo. Current Wegovy warnings include severe gastrointestinal reactions, pancreatitis, gallbladder disease, dehydration-associated kidney injury and hypoglycemia with insulin or insulin-releasing drugs. Its boxed warning concerns thyroid C-cell tumors observed in rodents, with human relevance unknown, and specified thyroid-cancer histories are contraindications. These are established product warnings, not a direct safety comparison with AOD9604.
An absence of the full growth hormone’s measured endocrine changes does not make AOD9604 generally safe. Equally, the existence of common semaglutide adverse effects does not establish that an incompletely studied alternative offers a better benefit-risk balance.
How to read the difference in clinical development
The main distinction is the outcome of controlled human testing. Semaglutide’s STEP 1 trial established additional weight reduction alongside lifestyle support. AOD9604’s larger oral trial did not establish the proposed obesity benefit, and the missing complete efficacy data prevent a precise quantitative estimate of what effect remains compatible with that study.
Semaglutide has approved product-specific indications and a defined safety framework. AOD9604 has no established approved obesity treatment in the selected official sources, and food-use or GRAS descriptions do not establish drug approval. For related mechanisms and the full formulation context, see the AOD-9604 profile, semaglutide profile and semaglutide versus tirzepatide comparison.
Frequently asked questions
Does the failed AOD trial prove an exact zero effect?
It failed to establish the intended obesity benefit. The available official summary does not provide complete estimates and confidence intervals, so it cannot establish equivalence to placebo or an exact zero effect.
Does food-use GRAS status mean an approved weight-loss drug?
GRAS means generally recognized as safe under specified food-use conditions. That description does not establish FDA approval of AOD9604 as an obesity medicine or validate an injectable preparation.
Do these studies compare current semaglutide tablets with injected AOD9604?
The principal results here concern injected semaglutide in STEP 1 and oral AOD9604 in OPTIONS. Changing both formulations creates a different comparison requiring its own evidence.
Where can I read the broader evidence?
The full AOD-9604 and semaglutide profiles linked below cover the growth-hormone-fragment program and current semaglutide products in more detail.
Profiles and related reading
References
- Stier H, Vos E, Kenley D. Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans. Journal of Endocrinology and Metabolism. 2013;3(1–2):7–15. DOI: 10.4021/jem157w.
Across six AOD9604 studies, the safety report did not find a rise in IGF-1 or worsening glucose tolerance overall. Its detailed results also include severe chest tightness and serious diarrhea considered possibly related to treatment.
- U.S. Food and Drug Administration. December 4, 2024 Pharmacy Compounding Advisory Committee Meeting. Official transcript, topic 2: AOD9604-related bulk drug substances.
FDA describes the 24-week, 502-person oral OPTIONS study as failing to establish greater weight loss than placebo despite diet and exercise support, and explains why the efficacy and safety information does not support an obesity treatment claim.
- Ng FM, Sun J, Sharma L, Libinaka R, Jiang WJ, Gianello R. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone research. 2000;53(6):274–278. doi:10.1159/000053183. PMID:11146367.
In genetically obese rats, AOD9604 reduced weight gain and increased fat-breakdown activity in adipose tissue. These animal observations did not establish a human obesity effect.
- Wilding JPH, Batterham RL, Calanna S, Davies M, Van Gaal LF, Lingvay I, McGowan BM, Rosenstock J, Tran MTD, Wadden TA, Wharton S, Yokote K, Zeuthen N, Kushner RF, STEP 1 Study Group. Once-Weekly Semaglutide in Adults with Overweight or Obesity. The New England journal of medicine. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183. PMID:33567185.
In STEP 1, 1961 adults without diabetes received semaglutide or placebo with lifestyle support. Mean weight fell 14.9% versus 2.4% at 68 weeks; more participants stopped semaglutide because of digestive adverse effects.
- Novo Nordisk. WEGOVY (semaglutide) injection and tablets: U.S. prescribing information. Revised June 2026. DailyMed; accessed October 15, 2026.
Wegovy activates the GLP-1 receptor and has product-specific approved indications. Its label describes approximately one-week elimination and important gastrointestinal, endocrine and other safety concerns.
- U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Agency assessment; accessed October 15, 2026.
FDA identifies immune-reaction and impurity concerns for PEG-MGF and AOD-9604. It reports no identified human exposure data for PEG-MGF and insufficient information to determine the safety of compounded AOD-9604.