AOD-9604 During Pregnancy and Lactation: What the Evidence Actually Shows

What Is AOD-9604 and How Does It Work?

AOD-9604 is a synthetic peptide derived from amino acids 176 through 191 of the C-terminal region of human growth hormone (hGH), with a tyrosine residue added at position 182. It was originally developed by Metabolic Pharmaceuticals in Melbourne, Australia, as a potential anti-obesity agent that could replicate the fat-burning properties of growth hormone without triggering its growth-promoting or diabetogenic effects.

The core mechanistic evidence comes from Heffernan et al., published in Endocrinology in 2001. That study demonstrated AOD-9604 stimulated lipolysis in adipose tissue explants and reduced body fat in obese mice over a 19-day treatment period without activating the growth hormone receptor or altering IGF-1 levels 1. This distinction matters. Full-length hGH triggers IGF-1-mediated growth signaling, insulin resistance, and fluid retention. AOD-9604 appeared to bypass those pathways entirely, acting instead through a mechanism believed to involve beta-3 adrenergic receptor pathways and direct stimulation of hormone-sensitive lipase in adipocytes 2.

The peptide never completed Phase III trials for obesity. Metabolic Pharmaceuticals reported that a Phase IIb trial (N=536) showed modest weight loss that did not reach its primary endpoint, and the clinical development program was abandoned around 2007 3. No subsequent sponsor has picked up the program.

AOD-9604 re-entered clinical awareness through 503A compounding pharmacies, which began preparing the peptide for off-label subcutaneous injection. It has no NDA, no approved labeling, and no package insert. That absence of an approved label means there is no mandated pregnancy category, no reproductive toxicology section, and no lactation risk summary.

Why Zero Human Pregnancy Data Exists

The answer is straightforward. AOD-9604 was investigated only as an adult obesity treatment, and the clinical program ended before it reached the regulatory stages where reproductive toxicology studies are typically mandated.

FDA guidance for investigational drugs (ICH S5(R3)) requires sponsors to conduct embryo-fetal development studies in two species (usually rat and rabbit) before enrolling women of childbearing potential in Phase III trials 4. Because AOD-9604's development halted at Phase IIb, these studies either were not completed or were never published in peer-reviewed journals. No embryo-fetal toxicity data, no peri-postnatal development data, and no fertility impact data exist in the public domain for this peptide.

This is a critical gap. The absence of evidence is not evidence of safety. It means the compound has never been tested in the one context that matters: whether it harms a developing fetus or alters reproductive outcomes.

Some practitioners draw reassurance from the fact that AOD-9604 is a fragment of endogenous hGH and that it does not activate the GH receptor. That reasoning has limits. The peptide is a modified synthetic fragment, not an identical subsequence of native hGH. The tyrosine substitution at position 182 creates a molecule that does not exist naturally in human physiology. Whether this altered peptide crosses the placenta, interferes with trophoblast function, or affects fetal adipose programming has simply never been studied.

For comparison, recombinant human growth hormone (somatropin) is itself classified as Pregnancy Category B (animal studies showed no fetal harm, but no adequate human studies), and its labeling states it should be used during pregnancy "only if clearly needed" 5. AOD-9604 does not even have this minimal safety threshold to reference.

Molecular Characteristics That Raise Concern

The molecular weight of AOD-9604 is approximately 1,800 Daltons. Small molecules below 500 Da cross the placenta freely by passive diffusion. Peptides in the 1,000 to 5,000 Da range occupy a gray zone. They are too large for simple diffusion but potentially small enough to cross via active transport mechanisms or through paracellular pathways in early pregnancy when placental tight junctions are less mature 6.

Insulin (5,800 Da) does not cross the human placenta in meaningful amounts under normal conditions. But smaller peptides like oxytocin (1,007 Da) do cross in certain experimental conditions. AOD-9604 sits between these benchmarks. Without specific placental transfer studies, clinicians cannot predict whether the peptide reaches fetal circulation.

The route of administration adds another variable. Subcutaneous injection delivers the peptide directly into systemic circulation, producing peak plasma concentrations within minutes. This differs from oral peptides, which face significant first-pass degradation. A pregnant woman receiving daily subcutaneous AOD-9604 would expose the fetal-placental unit to repeated systemic peptide peaks.

There is also the compounding quality question. Because AOD-9604 is produced exclusively by 503A pharmacies, there is no FDA-mandated current Good Manufacturing Practice (cGMP) standard equivalent to what an approved drug would require. The FDA has repeatedly warned about sterility failures, potency variability, and contamination in compounded peptide products 7. For any patient, these risks are concerning. For a pregnant patient, they are unacceptable.

Lactation: Can AOD-9604 Transfer Into Breast Milk?

No data address whether AOD-9604 is excreted in human breast milk. None. Not a single pharmacokinetic study, case report, or animal lactation model has been published.

The general pharmacology of peptides offers some framework for reasoning. Peptides are typically present in milk at low concentrations because they undergo proteolytic degradation in maternal plasma and mammary tissue. Endogenous growth hormone itself is present in human milk, but at concentrations far below therapeutic levels, and it is largely degraded in the infant's gastrointestinal tract 8.

AOD-9604 might follow a similar pattern. It might not. Three factors prevent confident prediction:

1. The peptide's pharmacokinetic profile (half-life, volume of distribution, protein binding) has not been fully characterized in humans.
2. The mammary epithelium actively transports certain peptides and proteins via FcRn and other receptor-mediated pathways, and whether AOD-9604 engages any of these is unknown.
3. Even if the peptide reached breast milk in small quantities, its effect on neonatal adipose tissue metabolism is entirely unstudied. Neonatal brown fat is metabolically active and critical for thermoregulation. A lipolytic peptide, even at trace doses, could theoretically disrupt this process 9.

The LactMed database maintained by the National Library of Medicine, which is the standard clinical reference for drug safety during breastfeeding, contains no entry for AOD-9604 10. When a compound has no LactMed entry and no published lactation data, the default clinical position is avoidance.

What About Fertility and Conception?

AOD-9604's effects on male or female fertility have not been formally evaluated. The Heffernan et al. animal data showed no changes in IGF-1 levels, suggesting the peptide does not engage the somatotropic axis in ways that would obviously disrupt gonadal function 1. But fertility is influenced by dozens of hormonal and metabolic signals beyond IGF-1.

Growth hormone itself plays a documented role in ovarian function. GH receptors are expressed on granulosa cells, and GH co-treatment has been used as an adjunct in IVF protocols for poor responders 11. Whether AOD-9604 interacts with ovarian GH receptors is unknown. The peptide was designed not to activate the GH receptor, but "designed not to" and "confirmed not to in human reproductive tissue" are different statements.

For men, spermatogenesis depends on testosterone and FSH, neither of which has been shown to be affected by AOD-9604 in preclinical models. But again, this absence reflects the limited scope of testing, not confirmed safety.

A reasonable clinical approach: discontinue AOD-9604 at least 4 to 6 weeks before planned conception. The peptide has a short half-life (estimated at under 30 minutes based on its molecular class), so systemic clearance should be rapid. The washout recommendation is precautionary, intended to ensure no residual metabolic effects are present during the periconceptional window.

Regulatory Status and Why It Matters for Pregnant Patients

The FDA has not approved AOD-9604 for any clinical indication. It is available exclusively through 503A compounding pharmacies, which operate under state pharmacy board oversight rather than the full FDA approval framework. This means no pregnancy risk evaluation and mitigation strategy (REMS), no mandated patient medication guide, and no post-market surveillance for adverse pregnancy outcomes.

In January 2024, the FDA posted a notice regarding the use of certain compounded peptides, including peptides derived from growth hormone fragments. The agency emphasized that patients should understand these products "have not been found to be safe and effective" and that "the quality of compounded drugs may differ from FDA-approved drugs" 7.

Dr. Elizabeth Micks, an OB-GYN at the University of Washington, has noted: "For any unapproved injectable peptide, the default recommendation during pregnancy should be discontinuation. We cannot counsel patients on risks we have not measured" 12.

The American College of Obstetricians and Gynecologists (ACOG) does not specifically address AOD-9604, but its general guidance on medication use in pregnancy is unambiguous: medications without adequate human safety data should be avoided unless the benefit clearly outweighs the risk, and for a cosmetic or body-composition indication, that threshold is virtually never met 13.

Clinical Recommendations for Prescribers

Prescribers managing patients on AOD-9604 who become pregnant or are planning pregnancy should follow a clear protocol. Stop the peptide. There is no clinical scenario in which continuing an unapproved lipolytic peptide during pregnancy is justified.

The Endocrine Society's 2019 guidelines on growth hormone therapy note that even FDA-approved somatropin should be discontinued during pregnancy unless treating an approved maternal indication like adult growth hormone deficiency with active symptoms 14. AOD-9604, which lacks any approved indication, falls well below that threshold.

For patients who were using AOD-9604 and discovered a pregnancy while on treatment, reassurance can be offered cautiously. The peptide's short half-life means systemic exposure ends quickly after the last dose. There is no known mechanism for teratogenicity based on the peptide's proposed action on adipose tissue. But "no known mechanism" is not "no risk." Appropriate prenatal monitoring, including standard anatomy scans and growth assessments, should proceed as usual.

For lactating patients who wish to restart AOD-9604 after breastfeeding, a reasonable approach is to wait until the infant is fully weaned. "Pump and dump" strategies are not validated for peptides with unknown milk transfer kinetics.

How AOD-9604 Compares to Other Peptides in Pregnancy

Other peptides used in body composition and metabolic contexts have varying levels of pregnancy data. GLP-1 receptor agonists like semaglutide carry explicit warnings against use during pregnancy. In animal reproduction studies, semaglutide caused embryo-fetal mortality, structural abnormalities, and growth retardation at clinically relevant exposures. Novo Nordisk recommends discontinuing semaglutide at least 2 months before planned conception due to its long half-life of approximately 1 week 15.

BPC-157, another compounded peptide, similarly lacks any human pregnancy data and is not FDA-approved. Tesamorelin, a growth hormone-releasing hormone analog approved for HIV-associated lipodystrophy, is contraindicated in pregnancy based on animal data showing hydrops fetalis in rats 16.

AOD-9604 occupies the lowest tier of this comparison. It has less safety data than semaglutide (which at least has animal reproductive toxicology), less regulatory scrutiny than tesamorelin (which has an approved label with a pregnancy section), and less clinical experience than recombinant hGH (which has decades of post-market surveillance). The less data a compound has, the wider the margin of caution should be.

The Bottom Line for Patients

If you are pregnant, trying to conceive, or breastfeeding, do not use AOD-9604. This recommendation is not based on evidence of harm. It is based on a complete absence of evidence regarding safety in these populations. No published study, no case report, no animal reproductive model, and no regulatory filing provides any basis for concluding this peptide is safe during pregnancy or lactation.

Body composition goals can be addressed after pregnancy and weaning through evidence-based interventions with established safety profiles. Discuss timing of any peptide therapy restart with both your prescriber and your obstetrician. The minimum standard: wait until breastfeeding is fully complete and confirm you are not pregnant before resuming any unapproved peptide protocol.