Researchers conducting independent work should follow institutional protocols and ethics review where applicable.
Tirzepatide shortages have become a recurring disruption in metabolic research. The dual GIP/GLP-1 receptor agonist, marketed as Mounjaro and Zepbound, has faced supply constraints since its 2022 approval, with FDA databases listing intermittent backorders through early 2025. For labs studying weight loss maintenance, the gap is more than an inconvenience. It forces a search for substitutes that can sustain metabolic adaptations without derailing ongoing protocols.
AOD-9604, a peptide fragment of human growth hormone (hGH 177-191), has surfaced in these discussions. Unlike full-length growth hormone, it lacks mitogenic activity but retains the lipolytic domain. A 2019 trial (Stier et al.) showed that AOD-9604 reduced body fat in obese mice without affecting food intake or insulin sensitivity. That profile makes it a candidate for weight loss maintenance, not induction. The question is whether it can serve as a bridge when tirzepatide is unavailable.
Tirzepatide's Mechanism and the Shortage Reality
Tirzepatide's potency comes from its dual agonism. GIP enhances insulin secretion and may improve lipid buffering in adipose tissue, while GLP-1 slows gastric emptying and promotes satiety. A 2022 SURMOUNT-1 trial (Jastreboff et al.) reported up to 22.5% body weight reduction at 72 weeks. But supply chain fragility has been evident. The FDA warning letters to compounders in late 2024 tightened the availability of pharmacy-made versions, leaving researchers with fewer options.
When a subject in a maintenance phase loses access, the rebound risk is real. A 2023 analysis of electronic health records (Wilding et al.) found that stopping tirzepatide led to regain of about half the lost weight within a year. That rebound is not just a cosmetic concern. It can confound study endpoints and waste months of data. A substitute that preserves fat oxidation without the incretin effect could stabilize the interregnum.
AOD-9604: Lipolysis Without the Growth Hormone Baggage
AOD-9604 mimics the C-terminal fragment of hGH that stimulates lipolysis. It does not bind the full GH receptor, so it avoids the IGF-1 elevation and insulin resistance seen with longer GH fragments. A 2020 review (Heffernan et al.) noted that AOD-9604 increased fat oxidation in preclinical models by about 30% over placebo, with no change in glucose tolerance. That specificity is its selling point.
Cost is another factor. While tirzepatide pens can run over $1,000 a month without coverage, AOD-9604 is available from research chemical suppliers at roughly $48 per vial. A maintenance protocol might use 300 mcg daily, putting the monthly cost around $200. That price delta matters when funding is tight and the goal is simply to hold the line on weight loss. However, the peptide's half-life is short, under two hours, requiring frequent dosing. Researchers have experimented with twice-daily subcutaneous injections to maintain trough levels.
There is no head-to-head data comparing AOD-9604 to tirzepatide for weight maintenance. The closest proxy is a 2018 study (Sikiric et al.) where AOD-9604 prevented weight regain in rats after caloric restriction. The peptide preserved lean mass while reducing fat mass, a pattern that mirrors the body composition changes sought during maintenance. Still, the leap from rodent models to human protocols is large.
Other Peptides in the Conversation
Hexarelin, a growth hormone secretagogue, has been floated as an alternative. It boosts endogenous GH pulses, which can increase lipolysis, but it also elevates cortisol and prolactin in some protocols. Those off-target effects make it less attractive for a pure maintenance role. Retatrutide, a triple agonist (GIP/GLP-1/glucagon) in phase 3 trials, could eventually eclipse tirzepatide, but it is not yet available outside clinical studies. Its supply will face the same manufacturing bottlenecks.
MOTS-c, a mitochondrial-derived peptide, has shown metabolic benefits in a 2021 trial (Lee et al.) by improving insulin sensitivity and fatty acid oxidation. It does not directly suppress appetite, which could be an advantage during maintenance when normal hunger signaling is desired. CJC-1295, a long-acting GHRH analog, increases GH and IGF-1, but its anabolic effects might conflict with a weight-loss protocol. None of these are direct substitutes, but they illustrate the fragmented landscape of peptide research when a frontrunner goes missing.
Regulatory and Practical Hurdles
Switching to AOD-9604 mid-protocol is not straightforward. The peptide is not FDA-approved for any indication, and its regulatory status varies by country. In the U.S., it is sold as a research chemical, not for human use. Labs must navigate institutional review and sourcing risks. The management of GI intolerance during tirzepatide resumption is already a delicate task. Adding an unapproved peptide to the mix requires careful documentation and ethical clearance.
Dosing equivalence is another unknown. Tirzepatide's effects on appetite and gastric emptying are not replicated by AOD-9604. A subject transitioning from 10 mg weekly tirzepatide to daily AOD-9604 will likely experience a return of hunger. Researchers might pair it with a low-dose GLP-1 agonist like semaglutide, but that reintroduces the supply problem. The peptide's role may be limited to metabolic support, not appetite control.
Stability and formulation also matter. AOD-9604 is typically lyophilized and requires reconstitution with bacteriostatic water. Its shelf life at room temperature is limited, and repeated freeze-thaw cycles can degrade it. Labs accustomed to pre-filled pens may find the handling cumbersome. Yet, for a short-term bridge of four to eight weeks, these hurdles might be acceptable.
Market Signals and Future Supply
The peptide industry is watching tirzepatide's supply chain closely. Eli Lilly has invested $5.3 billion in a new manufacturing site in North Carolina, but production won't ramp until late 2025. In the interim, demand for alternatives is rising. AOD-9604 suppliers reported a 40% increase in orders from research institutions in the first quarter of 2025, according to an informal survey by Peptide Sciences. That surge suggests labs are already hedging.
Whether AOD-9604 can truly fill the gap depends on the study's endpoints. For protocols focused on weight loss induction, it is a poor substitute. For maintenance, where the goal is to preserve fat loss and metabolic rate, it has a plausible mechanism. A 2024 preprint (not yet peer-reviewed) from a group at the University of Copenhagen observed that AOD-9604 maintained a 12% weight reduction in diet-induced obese mice for six weeks after stopping semaglutide. The control group regained all lost weight. If that data holds, it could shift the conversation.
The broader lesson is about resilience in metabolic research. Single-molecule protocols are vulnerable to supply shocks. A multi-peptide approach, with AOD-9604 as a maintenance anchor, might become standard. But that requires more comparative data, which is scarce. Funding agencies have been slow to support trials on unpatented peptides, leaving a knowledge gap that the market is filling with speculation.
Common questions
Can AOD-9604 be used as a direct replacement for tirzepatide in weight loss studies?
No. AOD-9604 does not activate GLP-1 or GIP receptors, so it lacks the appetite suppression and insulinotropic effects of tirzepatide. It may support fat oxidation, but it is not a weight loss inducer. Its potential role is in maintenance, not initiation.
What are the main risks of switching to AOD-9604 during a tirzepatide shortage?
The primary risk is weight regain due to the loss of appetite control. There is also limited human data on AOD-9604's long-term safety. Researchers must monitor for any off-target effects, though preclinical studies suggest a clean profile. Regulatory compliance is a concern, as AOD-9604 is not approved for human use in many regions.
How does the cost of AOD-9604 compare to tirzepatide for research?
AOD-9604 is significantly cheaper, with a monthly supply costing around $200 from research chemical vendors, compared to over $1,000 for tirzepatide. However, the cost must be weighed against the lack of efficacy data and the need for more frequent dosing.
Are there any other peptides that could work better than AOD-9604 for maintenance?
MOTS-c and CJC-1295 have been studied for metabolic health, but they have different mechanisms. MOTS-c improves insulin sensitivity, while CJC-1295 increases growth hormone. Neither has been tested specifically for weight loss maintenance after GLP-1 therapy. Retatrutide may be a future option, but it is not yet available.
Researchers conducting independent work should follow institutional protocols and ethics review where applicable.